We say "wait in line". When talking about a row of people or things, the article is usually, but not always, unnecessary.
We say "wait in line" (without "the"). When talking about a row of people or things, the article is usually, but not always, unnecessary.
Olivia had to wait in line for three hours.
She had to stand in line for two hours.
Additionally, omit the determiner to introduce the phrase "cut in line (without "the")". We use it when someone goes in front of other people who are waiting in line.
He cut in line in front of us.
Note that we omit the article to focus on the action (stand, wait, etc.) rather than the noun (line). Having said that, you can use "a", "the", or another determiner ("this", "that", etc.) to identify or quantify the noun in sentences like these:
The line is progressing.
It's a short/long line.