The abbreviation etc. is from the Latin et cetera, which means “and other things.” It appears at the end of a list when there is no point in giving more examples. Writers use it to say, “And so on” or “I could go on” or “You get the idea.”

In American English, etc. ends in a period, even midsentence. It is traditionally enclosed in commas when it doesn’t end a sentence, but nowadays the comma that follows etc. is disappearing. The 1979 edition of Strunk and White’s The Elements of Style insists that etc. be followed by a comma: Letters, packages, etc., should go here. But Bryan A. Garner’s 1998 edition of A Dictionary of Modern American Usage advises against a following comma, saying it is “more logical” to omit it: Carrots, potatoes, broccoli, etc. have the advantage of being vegetables. Garner’s point is that if we replaced etc. with something like and celery we would not follow celery with a comma.

All authorities agree that etc. is out of place in formal writing. The Chicago Manual of Style says that etc. “should be avoided, though it is usually acceptable in lists and tables, in notes, and within parentheses.” John B. Bremner’s Words on Words says, “Use it informally, if you really must.” Theodore M. Bernstein’s The Careful Writer says the term “has no place in writing that has any literary pretensions.”

Do not use etc. with a “list” that gives only one example; there should be at least two items listed. And never use etc. at the end of a series that begins with for example, e.g., including, such as, and the like, because these terms make etc. redundant: they already imply that the writer could offer other examples.

Every so often you’ll see and etc. But et means “and,” so and etc. would mean “and and so on.” Also to be avoided is etc., etc., because why do that, why do that?

Since cetera means “other things,” etc. should not be used when listing persons. For that, we have et al. (note the period), from the Latin et alii, meaning “and other people”: The Romantic poets Keats, Wordsworth, Shelley, et al., strove to capture man’s mystic relationship with nature.

All the rules for etc. apply to et al., including its unsuitability for serious writing.