Brackets (US)/Square Brackets (UK) […]
Brackets are used to explain or add information to something in a sentence or quotation.

Examples
The car retails for $16,995 [396,523,941 Vietnamese dong].
The play quotes frequently from the Mahabharata [an ancient Indian epic poem].
The president said: “We’re going to need to hire OOP [object-oriented programming] experts in the next year.”

Parentheses (…)
Parentheses show that the material inside the parentheses is less important than the main part of the sentence. Often you can replace them with commas, but parentheses make the material seem less important.

Examples
The world’s leading automakers (Toyota, Volkswagen, and General Motors) are all pursuing hybrid technology.
Jennifer’s cat (an angora) is very friendly.
Germany’s decision to invade the Soviet Union (in 1941) led to disaster.