encapsulation

The nesting of headers: each layer passed puts its own around what it received. Transport adds the ports, IP adds the addresses, the link adds the MAC addresses. ping counts it in front of you — 56(84) bytes of data says 56 bytes of payload became 84 on the wire, 8 of ICMP header and 20 of IP header having been added. The order of the envelopes is also the order of addressing: a port names a program, an address a machine, a MAC the next neighbour.