What is the difference between type k and type L copper?

Type K has a thicker wall than type L. Type K is usually used underground and type L is used in Commercial buildings. Type M is usually used in Residential Buildings.

M tubing is very thin and in decent codes it is not allowed except for possibly heating.

L tubing is used for water supply ABOVE ground for both residential and commercial

K tubing having the heaviest wall thickness of copper TUBING is used for under ground applications