lock in
verb
Definitions
To secure (someone or something) in a locked enclosure.
To fix the value of something potentially variable.
Example: I've locked in a rate of 5%.
noun
Definitions
A sleepover party, usually held in a public place such as a church or school, in which the participants are not allowed to leave until the next morning.
Example: The youth group will have their annual lock-in this weekend.
An illegal but widely-tolerated invitation-only gathering in a British pub, after the end of licensing hours, to allow regular customers the opportunity to enjoy further drinking time.
A situation in which members of an industry have agreed to adopt a certain standard and have retooled their production to meet this standard, thus making it very costly to change to a different standard.