I divide NAT into two different types: Source NAT (SNAT) and Destination NAT (DNAT).
Source NAT is when you alter the source address of the first packet: ie. you are changing where the connection is coming from. Source NAT is always done post-routing, just before the packet goes out onto the wire. Masquerading is a specialized form of SNAT.
Destination NAT is when you alter the destination address of the first packet: ie. you are changing where the connection is going to. Destination NAT is always done pre-routing, when the packet first comes off the wire. Port forwarding, load sharing, and transparent proxying are all forms of DNAT.