An acronym (from Ancient Greek ἄκρος ákros "top, edge" and ὄνομα ónoma, Doric and Aeolian ὄνυμα ónyma, "name") is a special case of the abbreviation. Acronyms are created by shortening words or groups of words to their initial parts.
There are two competing definitions of the term acronym:
According to the great dictionaries of German, e.g. B. Duden and Wahrig, an acronym is an abbreviation that is composed of the first letters of several words, with EDP (electronic data processing) being mentioned as an example. ADAC , PC and TÜV are therefore acronyms, since they consist of the first letters of the expressions on which they are based. No acronyms are abbreviations such as abbr., lt., betr. or cpl.
Further definitions can be found in specialist lexicons of linguistics: " Abbreviation formed from the first letters or syllables of a word group or compound , which is used as a word."  The linguist Hadumod Bussmann defines the term accordingly.  In contrast to the first definition, not only initial letters but also (abbreviated) initial syllables are taken into account here.
Bussmann divides acronyms into different types:
Duden, Wahrig and Bußmann and Glück  treat initial word as a synonym for acronym. According to Duden and Wahrig, an initial word is a special form of the letter word (see below), which consists only of the first letters, i.e. the initials of the words. For example, the initial word LASER stands for Light Amplification by Stimulated Emission of Radiation. According to Bußmann and Glück, the syllable abbreviation is also an acronym.
Names can also be used as the basis for initial words. In the case of the Alwegbahn, named after A xel L ennart Wenner - Gren, an association with “all paths” was also intended.
Syllable abbreviations (also syllabic words) are abbreviations consisting of the first syllables of the underlying expressions: Kripo for criminal police, Trafo for transformer, Elko for electrolytic capacitor . These are related to head words, such as auto for automobile or accumulator for accumulator, and tail words, such as bus for omnibus.
A similar short form is formed from the beginning of several words. For example, Haribo stands for Ha ns Riegel from Bonn (candy manufacturer) and Chipitts for the region around the cities of Chicago and Pittsburgh in the USA. Compositions that are easy to speak are often used here.
More examples of syllable abbreviations:
An apronym is an acronym that makes up an existing word. This means that potentially any word can become an apronym if the individual letters can be used as the first letters of a phrase. Most apronyms have an intentional relation to the thing they denote. Examples:
Apronyms often serve as names for EU funding programs or US laws. For example, ERASMUS stands for E u r opean community action s cheme for the mobility of university students or LEADER for Liaison entre a ctions de d éveloppement de l ' é conomie r urale. The abbreviation USA PATRIOT Act stands for Uniting and Strengthening America byProviding Appropriate Tools Required to Intercept and Obstruct Terrorism.
A backronym [ˈbækɹənɪm] (“backward apronym ”) is a term used to describe words that only subsequently received the (often joking) meaning of an abbreviation. Examples of this:
An acronym can be multi-layered (nested). An example of this is BDSM : B& D, D &S, S&M stand for B ondage & Discipline, Domination & Submission, Sadism & M asochism.
A recursive acronym is an acronym or abbreviation that refers to itself in explaining its meaning. Recursive acronyms are often found in computer engineering. Examples:
There are various forms of words that resemble acronyms without satisfying either of the two definitions given.
A letter word is similar to the initial word, but is made up of any individual letters in the full form of the word: for example DAX as an abbreviation for German stock index, where the last letter of the abbreviated source word is taken into account. [8th]
→ See also: "Abbreviations without periods and spaces" in the article: Abbreviation
Acronyms are usually spelled out as a series of capital letters. Over time, however, acronyms that are pronounced like a word have also developed a spelling similar to that of normal nouns (e.g. Radar, Laser, Aids, Nato, Unicef ; but not KKW, SMS, HIV, US ). Since acronyms are written without a period, in such cases it is not recognizable either from the pronunciation or from the typeface that it was originally a made-up word acts; however, this reflects the pronunciation in the typeface.
On the Internet, acronyms are often used to express an action or a state of mind. So LOL (Laughing Out Loud) is the name when a chatter has to laugh. ROFL (Rolling On [the] Floor Laughing) is another step up, in which case the chatter can hardly contain himself from laughing. Like these two examples, most chat acronyms are borrowed from the English language. Another commonly used acronym is AFK (Away From Keyboard), used to communicate a temporary absence. Also commonly used on forums IMHO (In My Humble/Honest Opinion) and AFAIK (As Far As I Know).
Terms like “cu” or “l8r” are not acronyms, but homophonic abbreviations, which means they sound like the sentence to be expressed (see you, later), but are not initial words.
To mark words as abbreviations on websites , the two HTML elements abbr(from English abbreviation "abbreviation") and acronymare available.  Screen readers recognize these elements. You no longer need to "guess" whether a word is an abbreviation, but adjust the pronunciation accordingly. Both elements can be assigned what the abbreviation stands for. This can then be played back by a screen reader instead of the short form. Choosing between abbrand acronymgives the program an indication of whether the abbreviation is a word - acronym- or individual letters -abbr- should be read.
It is recommended by the World Wide Web Consortium abbr to use as a priority. However, this simplification comes at the expense of accessibility. Acronyms that should actually be spoken as a word are no longer recognized as such.
In general, abbreviations, including acronyms, are used with the same meaning as the expressions on which they are based (= full forms). Deviating from this, the plural can also be formed with -s.  Word formation also opens up special possibilities with acronyms: One can form a -ler derivation that is not possible with the full form: SPDler.
However, the principle of the equivalence of full form and acronym with regard to their meaning presupposes that the user is also familiar with the full form. If this is not the case, there can be a change in meaning and lexicalization. Lexicalization tendencies can be seen, for example, in the designation BAföG, which is usually understood as a monetary benefit and no longer as the underlying Federal Training Assistance Act.
The situation is similar with “SMS”: “SMS” means Short Message Services and describes the service that enables short messages to be sent. So the message itself would be more of an “SM” (or “short message”). Nevertheless, it has become common practice to refer to the message as "SMS", especially since the correct abbreviation (" SM ") has already been taken in general usage.
There are critics who reject word formations such as LCD display, since the “D” in the abbreviation already stands for display (Liquid Crystal Display). The situation is similar with the HIV virus, where the “V” already stands for “virus”, the ABM measure (ABM = job creation measure), the CSS style sheet (CSS = cascading style sheet), the PDF format (PDF = Portable Document Format) or the PIN number (PIN = Personal Identification Number).
For this reason, in German commercial law, a GmbH (limited liability company) is referred to as a mbH if the term "company" is already in the company's proper name (e.g. Württembergische Eisenbahn-Gesellschaft mbH).
In English, this redundancy is referred to recursively as “RAS Syndrome” (Redundant Acronym Syndrome Syndrome). These duplications can be seen rhetorically as a tautology (as a statement) or as a pleonasm (as an expression).