a couple of (things)
"A couple" means two, or approximately two.
"A couple of weeks" means two weeks. But "a couple" is not as exact as "2", so you might say "a couple of weeks ago" if something happened recently but you don't remember exactly when.
Sometimes we leave out "of" in spoken English:
I'll be there in a couple minutes.
In writing, though, we almost always include "of".
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