Parentheses ( ) (from Greek paren = round, thesis = thingies), also known as round brackets, curved brackets, oval brackets, or just brackets (or, informally, parens, or fingernails) are punctuation marks (more specifically, rounded brackets) used in the English language (in other words, they are found in no other language) for additional yet unnecessary information in writing without (in theory) disrupting the flow of main text. They may also be used for supplementary information, sources of anal-retentiveness for High-School English teachers, parenthetical citation (in writing where citations are necessary), and clarification of the possible plurality of nouns, such as "I burning your dog(s)". Additionally, a set of parentheses may contain parenthesis, like this: "A man inserts his penis (also known as a "cock" (which also means rooster) in slang) into the pencil sharpener." The set within the set (usually) can be substituted with brackets (you know, those [ ] things).
Any punctuation inside parentheses is independent from the rest of the text: "David (What a piece of shit that guy was. Seriously.) was the team captain back in high school." The only exception to this is the case where parenthesis are at the end of a sentence, in which case a period at the end of the statement within the parenthesis is not required (ending punctuation may be found after the parenthesis).
The number of parenthesis (within a parenthesis) may be infinite, but this is highly discouraged as it may lead to loss of focus on the initial topic. For example:
"Bob has a big (though not very long, it has some girth (too bad the same can't be said for his testicles (speaking of which, those things are hairy), which are like little peas (I hate peas) in a sac) which compensates for his stump dick).) penis." The initial topic was about squirrels.
In mathematics, parentheses signify a different precedence of operators and can represent a binomial coefficient (whatever that stuff means).