An abbreviation is a shortened form of a word or phrase. Depending on the abbreviation, it may be written in uppercase, lowercase, or a combination of upper- and lowercase letters. It may or may not include one or more periods.
An abbreviation is a shortened form of a word or phrase. Depending on the abbreviation, it may be written in uppercase (ID), lowercase (tsp.), or a combination of upper- and lowercase letters (Mrs.). It may or may not include one or more periods.
An acronym is a specific type of abbreviation. Acronyms are formed from the first letter or letters of the words in a name or phrase, sometimes producing a pronounceable word (AIDS, NATO, NASA, JAMA), and sometimes not (ATM, CEO). In the United States, acronyms are usually set in all capital letters.
Sometimes an acronym will enter the language as a word with its own meaning, such as scuba, from self-contained underwater breathing apparatus.