Refers to the way the data is stored in memory.
Bytes order: Byte3 Byte2 Byte1 Byte0
Little Endian is stored from right to left. (Least significant bit is stored to the lowest address in memory)
Big Endian stored from left to right (most significant bit is stored to the lowest address in memory)
Reference
http://people.cs.umass.edu/~verts/cs32/endian.html
Least significant bit
http://en.wikipedia.org/wiki/Least_significant_bit
Most Significant Bit
http://en.wikipedia.org/wiki/Most_significant_bit