What is big-endian and little-endian?

Suppose, 32 bits Data is 0x11223344.

Big-endian

The most significant byte of data stored at the lowest memory address.

Little-endian

The least significant byte of data stored at the lowest memory address.

Note: Some processor has the ability to switch one endianness to other endianness using the software means it can perform like both big-endian or little-endian at a time. This processor is known as the Bi-endian, here are some architecture (ARM version 3 and above, Alpha, SPARC) who provide the switchable endianness feature.