Abbreviation, it is a word of Latin origin that implies reducing the writing of the words in their extension, in order to save time and space; which must be done in a conventional way, if these abbreviations are to be known and understood by all. So we all know that Mrs. is the abbreviation for Mrs., or that Dr. is the abbreviation for doctor, but nothing prevents a person from creating for his personal use a series of abbreviations that he only knows, such as those used in taking notes, since they are for personal use, and allow faster copying of the ideas that are heard and that are intended to be captured on paper.
For example: "In a scientific paper, do not use abbreviations, unless they are standard and do not hinder the understanding of the text", "They failed me for a monograph for putting the words with their abbreviations, and, in addition, they told me that they were not the accepted ones", "Do not use abbreviations in the title of a report, or when you start the sentence" or "I would lend you my note taking, but you would not understand my abbreviations, because they are invented".
Abbreviations are written with a full stop, according to the Royal Spanish Academy, unless they are placed in parentheses or the sentence ends with them, since in this case the full stop of the sentence replaces the full stop of the abbreviation. The accents of the words they replace must be kept, if they had them. For example, the page abbreviation is p. In general, they are written in capital letters, although in many cases they depend on the context Mrs. (Mrs.) D. (Mr.) Dr. (doctor) They are always written in capital letters, but etc. (etc.) or p. (page) are generally lowercase.
If the abbreviation corresponds to words that have variation in their gender, they replace both the feminine and the masculine, for example, "it" can correspond to Italian or Italian. If you want to express that it is a plural, you must add an "s" at the end.
If we delete the final part of the word, it is called abbreviation by truncation, which in our language should not end in a vowel, for example, when we write etc. by etcetera or agric. by agriculture, or Tel. by phone. When some letters of the word located in its middle are removed, it is called abbreviation by contraction. This happens for example with atto. by attentive, or Vda. by widow. It can also be abbreviated with the initial letters of the words and this is called an acronym such as OEA (Organization of American States).