The subject of abbreviation, abbreviation and acronym is in the context of word formation which also covers derivation and composition.
Abbreviation
The abbreviation of the word is also known as the reduced form of the word and comprises the reduction of the word to a limit, so that there is no harm to understanding.
Let's look at some examples:
Moto – motorcycle
Micro – microcomputer
Phone – telephone
Photo – photography
Tire – pneumatic
Cine – cinema
Abbreviation
Abbreviation is the representation of a word through its syllables (usually initials) or letters. To know how to correctly abbreviate a word is simple: write the first syllable and the first letter, followed by the abbreviation period.
If the first letter of the second syllable is a vowel, the
abbreviation will go up to the consonant. If the word has a graphic
accent on the first syllable, it will be kept and if the second syllable
starts with two consonants, it will be kept in the abbreviation.
There are still cases that do not obey any particular rule.
Let's look at some examples:
Gram. – Grammar
m – meter
adj. - adjective
no. – numeral
no. –
Gen number.
– personal gender – person
a. C. – before Christ
apt. – apartment
Co. –
Ltd. – limited
SA – limited liability company
id. – ditto
ib. or ibid. – ibid. (in the same way)
USA – United States of America.
vv. - verses
Acronym
The acronym is very common, especially in scientific and journalistic texts in general.
There are rules regarding the use of acronyms: all letters must be capitalized if the acronym has up to three letters or if all the letters have an independent meaning:
CEP – Postal Address Code
UN – United Nations
Organization NGO – Non-Governmental Organization
MEC – Ministry of Education and Culture
CEF – Caixa Econômica Federal
BB – Banco do Brasil
INSS – National Institute of Social Security
IOF – Tax on Financial Operations
SIF – Service of Federal Inspection
If the acronym has more than three letters, only the initial will be written in capital letters.
Detran – State Traffic Department
Unesco (United Nations Educational, Scientific and Cultural
Organization) – United Nations Educational, Scientific and Cultural
Organization
Embrapa – Brazilian Agricultural Research Corporation
Bovespa – São Paulo State Stock Exchange
Volp – Orthographic Vocabulary of the Portuguese Language
Source: https://mundoeducacao.bol.uol.com.br/gramatica/abreviacao-abreviatura-siglaqual-diferenca.htm
* Non-standard abbreviation and acronym should be translated in a footnote.
Graphical accentuation of the word is kept in the abbreviation Ex: p.
A sentence that ends with an abbreviated word does not have a full stop. etc. and not etc.