They are reducing speed.
3 seconds sound clip from the Star Trek II: The Wrath of Khan movie soundboard.
You can hear this line at 01:24:57 in the Blu-ray version of the movie.
Quote context
[...]
- Remind me to explain to you, the concept of the human ego.
- One minute to nebula perimeter.
- Daren't follow them into the nebula, sir. Our shields would be useless.
- Aye, sir. You're on, Admiral.
- This is Admiral Kirk. We tried it once your way, Khan. Are you game for a rematch?
- I'm laughing at the superior intellect.
[...]