The scholarly et al. means "and others." Say you’ve got an article written by Crosby, Stills, Nash, and Young. You can take a scholarly shortcut and refer to them as "Crosby et al.."
The phrase is an abbreviation for the Latin et alii. You don't need a period after et, since that's the whole word, but you do need a period with al.. Something else you need to know is that you don't use a comma between the proper name and the abbreviation, just as you wouldn't use a comma if you were writing "Crosby and others." And one last thing: you don't usually italicize et al., even though it's Latin.
