Lock and Key 

It"s usually used when you're talking about your best friend meaning he/she holds you together and keeps you in check. Also could mean you two belong together.

she is my lock and key, i don't know what i'd do without her.

Lock and Key by bathtub queen April 4, 2017

Lock and Key 

The act of performing anal sex on a woman and being able to tell anyone in a very clean and discreet manner. It is also a way for a woman to show her man that she is willing to go above and beyond the call of duty to please him.

"Hey bro....i got the Lock and Key from my girl last night."

"Baby, when are you going to let me get that Lock and Key?"

As I approached the bedroom, little did i know that she had the lock and key waiting for me.

Lock and Key by daddyof2lilshiz August 12, 2011

lock and key theory 

The lock and key theory was dreamt up in Liverpool, England by an un-named genius. It states that a guy is like a key, and a girl is like a lock. A key that opens many locks is a master key, yet a lock that is opened by many keys is a shitty lock. This theory is rarely favoured by females... for some reason.

The lock and key theory is most suitably used to shut a girl up that complains about male sexual promiscuity being praised by peers, while that of a female is frowned upon. Works every time.

lock and key theory by mw2_360 December 12, 2009

lock someone up and throwaway the key 

to be sentenced to life in prison without the possibilty of parole

i wanna lock someone up and throwaway the key.

lock someone up and throwaway the key by buba1234 March 7, 2012