In digital computer programming, a bitwise operation operates on one or more bit patterns or binary numerals at the level of their individual bits. It is a fast, primitive action directly supported by the processor, and is used to manipulate values for comparisons and calculations.
There are a number of bitwise operators, which deal with the binary interpretation of PHP integers.
& is a bitwise AND
| is a bitwise OR
^ is a bitwise XOR
~ is a NOT, which means it inverts all bits
<< is a left shift >> is a right shift
See also: http://en.wikipedia.org/wiki/Bitwise_operation