a mark (‸) made in written or printed matter to show the place where something is to be inserted.
a symbol (∼) indicating equivalency or similarity between two values.
a printed punctuation mark (‽), available only in some typefaces, designed to combine the question mark (?) and the exclamation point (!), indicating a mixture of query and interjection, as after a rhetorical question.
The word a or an introducing an unspecified noun or the name of a general category: “a dog,” “an apple,” “an orange.” An is used when the next word begins with a vowel or a silent (unpronounced) h, as in “an egg” or “an hour.”