From Longman Dictionary of Contemporary Englishlock in phrasal verb1 KEEP somebody IN A PLACE 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. → lock→ See Verb table
Examples from the Corpus
lock in• Some families are locked in a cycle of poverty.From Longman Business Dictionarylock in phrasal verb1[transitive] lock something → inFINANCE to gain something and be certain to keep itInvestors can lock in an 8.4% yield on a 30-year Treasury Bond.Venezuela is seeking to lock in buyers for its oil.2[intransitive] to come to a firm agreement that will last for some time and cannot be brokenMany homeowners are keen to lock in at current low interest rates. → lock→ See Verb table 