Pinging www.some-domain.com [XXX.XXX.XXX.XXX] with 32 bytes of

Reply from XXX.XXX.XXX.XXX: bytes=32 time=564ms TTL=237
Reply from XXX.XXX.XXX.XXX: bytes=32 time=555ms TTL=237
Reply from XXX.XXX.XXX.XXX: bytes=32 time=554ms TTL=237
Reply from XXX.XXX.XXX.XXX: bytes=32 time=548ms TTL=237

Ping statistics for XXX.XXX.XXX.XXX:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss)
Approximate round trip times in milli-seconds:
Minimum = 548ms, Maximum = 564ms, Average = 555ms

whats TTL?