key
A groove in the top of a footing. 

keys
Little fingers of plaster that squeeze through lath. When they harden, these hold the plaster in place. 

keystone
An angular block centered over a door or window in a header or mantle. 

kick-out clause
A clause in a sales contract that allows a seller to accept one buyer's contingent offer, then back out without penalty if a second buyer makes a better offer. 

kit home
A structure that contains prefabricated components and is put together by a contractor. 

knee wall
A wall-like structure that supports roof rafters.