[mmooss]

Many people don't use semicolons (;) in English but many do, and they are certainly part of correct grammar.

Semicolons are generally alternatives to periods, when you want more connection between the two sentences. Like periods, semicolons must have two full sentences—that is, what could be full sentences—on either side of them; the potential 'full sentences' are properly called independent clauses. (A dependent clause needs the rest of the sentence to form valid grammar; it can't function on its own. For example, in this paragraph's first sentence, when you want more connection between the two sentences is a dependent clause. Often they follow commas.)

Another use of semicolons is for lists in a paragraph where one of the list items has a comma in it (similar to the parsing problem for CSVs where some records contain commas): I only like wine; beer, but only ales; and orange juice.