lock in phrasal verb ( see also ↑ lock )
1 . lock somebody in (something) to prevent someone from leaving a room or building by locking the door:
She locked herself in.
They locked the director in his office.
2 . lock something ↔ in to do something so that a price, offer, agreement etc cannot be changed:
Sell your stocks now to lock in some of the gains of recent months.
3 . lock something ↔ in to make the taste, liquid etc remain in something:
This method of cooking locks in the flavour of the meat.