pod

The museum is a massive zigzag-shaped edifice constructed of five interconected pods - each pod larger than a football field. - The Lost Symbol - D. Brown
Could you explain which meaning does the word pod have in this context?

Thank you for your help

A pod is a type of compartment which is often self-contained, detachable or modular (i.e. a number of identical pods may be joined together to make a larger structure). Here is M-W's definition:

a usually protective container or housing:
as
a : a streamlined compartment (as for fuel) under the wings or fuselage of an aircraft
b : a compartment (as for personnel, a power unit, or an instrument) on a ship or craft

They are not usually very large, so the ones in the book are unusual. They may often be rounded in shape, rather like a seed pod (from whence the term is derived).