MTU defines the largest packet size that can be sent over a network connection. A higher MTU allows for more data to be transferred at once; connections with high MTUs typically have more bandwidth than connections with lower MTUs.
On TCP/IP networks, the Network layer protocols (such as IP) can perform an additional function called fragmentation, which subdivides the segments it receives from the Transport layer into smaller packets. It ensures that packets issued to the network are no larger than the network's maximum transmission unit (MTU) size.