An abbreviation is, prior convention that is made in a language for this purpose, the use of one or more letters of a word with the aim of making them shorter for a text and that the same continues to be understood by that of the convention. The methodology to create them is the elimination of some of the final or central letters or syllables of the word in question, for example United Nations Organization (UN).
It is that since we were little, we just began to emerge the vice of reading, in the subject of language and literature at school, the subject of abbreviations is an undisputed ball and has always been present, since many, books, writings, newspapers, magazines, dictionaries that we will face in the future will have in their texts a very large number of abbreviations, which in the case of not knowing them will of course complicate the understanding of it.
There are two ways to abbreviate a word, one by truncation and the other by contraction. Truncation implies the elimination of the final part of the word, for example av. by avenue, meanwhile, the abbreviations that are made following this modality can never end with a vowel. And contraction abbreviations are those in which the central letters of the word are eliminated, leaving only those that are most representative of it. In this case it would be Avda. by avenue. Oh and always, always the abbreviations must be accompanied at the end by a period, which is what ends up confirming that we are dealing with a full-fledged abbreviation.
Meanwhile, there are some abbreviations that have achieved a notable extension of their use that has made them transportable abbreviations even from one language to another, for example: AC (Before Christ), etc.: Etcetera.
It is also necessary to mention that abbreviations in many cases have the function of making a certain text more functional, simple and fast, that is, they have the objective of making a piece of writing more functional, but be careful, according to the RAE, their use cannot be indiscriminate but effective. You must delete at least two letters from the word that is abbreviated, they must not be used in quantities when they are expressed in letters.