The TTL is the number of iterations or transmissions that a packet can make before a network device discards it. "TTL" stands for "time to live."
In a computer network, large pieces of data typically break up into smaller pieces, which are known as packets. These packets transmit from device to device with a TTL set for the packet. With every transmission, the TTL for the packet reduces until the value is equal to zero. Once the TTL for the packet reaches zero, and it has not yet reached its destination, the packet and all of its data is discarded.