Digital Logic and Assertion levels
Assertion level is the voltage level in a logic circuit that represents a logical "1". Common level for high = +5v and low = 0v. A logical AND circuit that operates with assertion high (also called positive AND) requires high level on all inputs to yield a high output. If you change your terms of reference to assertion low, then the exact same circuit becomes an OR - any low input yields a low output (also called negative OR).

Positive AND == Negative OR