What is a baffled liquid tank, as described in the CDL manual?

49 CFR 383.119(c); AAMVA CDL Manual Section 8.2.4, 'Baffled Tanks,' p.8-8-2

Knowing what a baffle actually is, holes in internal dividers rather than a solid wall, explains why baffled tanks behave differently in traffic than fully open or fully sealed designs. That difference directly affects how a driver should brake, turn, and accelerate.