B2
the period of time during which someone lives or something exists:
We'll see a tremendous lot of technological changes during/in our lifetime.
Winners of the competition will receive the holiday of a lifetime (= the best holiday they will ever have).
I've only been working here two days, but it seems like a lifetime.
A watch of this quality should last a lifetime.
Enter our competition and this once-in-a-lifetime experience could be yours!
Marriage is no longer always seen as a lifetime commitment.
You could win a lifetime's supply of toothpaste.