a period of time; for a while; at one time
Refers to a distinct, often temporary, period in the past or future. As an adverb, it means 'for a certain period' or 'at one time'.
He worked abroad for a period of time.
At one time, that shop was very popular.
I used to smoke for a while, but I quit now.
There was a period when things weren't going well at work and I was troubled.