Why is the basic mesh unit always a pyramid ?

HI all:
why is meah basic unit always pyramid ?
I always see in FEM simulation .
Any reference I can read ?

thanks a lot

Hi myem,

You can refer to:
Numerical Techniques in Electromagnetics, Second Edition by Matthew N.O. Sadiku (Hardcover - Jul 12, 2000)

It's good book for FEM and MoM.

regards!