https://www.merriam-webster.com/dictionary/break-i Noun
Definition of break-in
1 : the act or action of breaking in a rash of break-ins at the new apartment house
2 : a performance or a series of performances serving as a trial run
3 : an initial period of operation during which working parts begin to function efficiently
See break-in defined for English-language learners
Definition of break in
intransitive verb
1 : to enter something (such as a building or computer system) without consent or by force
2 a : intrude break in upon his privacy
b : to interrupt a conversation
3 : to start in an activity or enterprise breaking in as a cub reporter
transitive verb
1 : to accustom to a certain activity or occurrence break in the new clerk
2 : to overcome the stiffness or newness of break in a pair of shoes