colon
The mark that introduces what explains, completes, or lists what came before it.
A colon follows a complete clause and introduces material that the clause has prepared the reader for: an explanation, an example, a list, or a quotation. That material may be a single word, a phrase, or a full sentence, but whatever comes before the colon must stand as a sentence on its own. A colon never separates a verb from its object or complement, or a preposition from its object. Capitalization after a colon. Each other use of the colon has its own entry, listed under Colon.
Examples
UseThe decision was simple: we would close early. (The clause before the colon is complete, and what follows explains it.)
UseShe had one goal: speed. (A single word can follow the colon when the clause before it is complete.)
UseThe kit includes three tools: a hammer, a wrench, and pliers. (The complete clause announces the list that follows.)
AvoidThe kit includes: a hammer, a wrench, and pliers. (The colon separates the verb includes from its objects; drop the colon.)