The refers to the area located in the oil pan and timing chain part of the engine cylinder block
assembly.

A. Sump
B. Block underside
c. Offset area
D. Balance shaft

The Block underside is the area located in the oil pan and timing chain part of the engine cylinder block

Explanation:

A block is a holding of the cylinder bores by metal, the water cooling jacket, passage of oil, and the crankcase. The engine block is secured on the top by the cylinder head. At this time the pistons attached within the cylinders move up and down which turns the crankshaft, and that ultimately drives the wheels.The place where the oil pan and timing chain part of the cylinder block assembly is called the block underside. These areas are fully covered by the timing chain cover and the oil pan cover, which are stamped sheet metal assemblies or cast aluminum assemblies.  

Iactually don’t know but i know someone you can ask