Network Address Translation.

[IETF] RFC1918 defines three address ranges that may be used for so-called ''private'' networks.  These ranges must not be forwarded by [Router routers] onto the general [Internet].

NAT (see RFC1631) defines a means by which a router can translate the source or destination IP Address in forwarded packets to make a private network appear to be a single host with a public network address.

{http://static.howstuffworks.com/gif/nat-router.jpg How NAT works}

Many [CableModem], [ADSLModem] and [AccessPoint] devices include a NAT [Router].