BitAnd[, , ... ] gives the bitwise AND of the integers .
Integer mathematical function (see Section A.3.10).
BitAnd[, , ... ] yields the integer whose binary bit representation has ones at positions where the binary bit representations of all of the have ones.
For negative integers BitAnd assumes a two's complement representation.
See The Mathematica Book: Section 3.2.4.
See also: BitOr, BitXor, BitNot, And, IntegerDigits, DigitCount, CellularAutomaton.