Endianness refers to the way that a computer processor or file format stores numbers.
Big endian numbers are stored in such a way that the most significant digit appears first in the number as it is read from left to right. This is familiar to most people as it is the way that nubers are represented in most languages. For example, in the number 1337 the first digit is the most significant digit because it represents 1000 units. The last digit is the least significant because it only represents 7 units.
Little endian numbers are stored in such a way that the most significant digit appears last in the number as it is read from left to right. When the number 1337 is stored in a little endian system, the seven is the most significant digit and represents 7000 units. The one is now the least significant digit representing only one unit.
When examining numbers in hexadecimal form on a little-endian system, the byte order must be reversed before converting to decimal. Note that the individual characters within the byte are not reversed because the whole byte represents one number. For example, the hexadecimal number 39 05 must be reversed to 05 39 before being converted to the decimal 1337.
x86 processors usually represent numbers in little endian form. PowerPC processor architectures tend to be big-endian.