TTL field IPv4

The TTL (Time To Live) field in the IPv4 header is not exactly the Hop Counter.
It is actually the maximum lifetime of an internet packet in the internet."

Extract from RFC791 - Internet Protocol

Time to Live:  8 bits

   This field indicates the maximum time the datagram is allowed to
   remain in the internet system.  If this field contains the value
   zero, then the datagram must be destroyed.  This field is modified
   in internet header processing.  The time is measured in units of
   seconds, but since every module that processes a datagram must
   decrease the TTL by at least one even if it process the datagram in
   less than a second, the TTL must be thought of only as an upper
   bound on the time a datagram may exist.  The intention is to cause
   undeliverable datagrams to be discarded, and to bound the maximum
   datagram lifetime.

http://www.faqs.org/rfcs/rfc791.html