What is the difference between SIP trunking and VOIP?

Please do not confuse about what is the difference between SIP trunking and VoIP. Let we understand this in simplest laymen’s terms the practical answer.
1. VOIP "voice over IP" is a standard term used to cover all voice traffic over the internet protocol.
2. SIP trunking is just voice over IP, using the SIP signaling protocol, but instead of using a single SIP user the VoIP service provider is providing many. Basically like a T1E1 link, but using VoIP with multiple trunks.
The Session Initiation Protocol (SIP) is an application-layer control protocol for creating, modifying, and terminating sessions with one or more participants. It can be used to create two-party, multiparty, or multicast sessions that comprise Internet telephone calls, multimedia distribution, and multimedia conferences.
Voice over Internet Protocol, also called VoIP, IP Telephony, Internet telephony, Broadband telephony, Broadband Phone and Voice over Broadband is the routing of voice conversations over the Internet or through any other IP-based network.
It gives VOIP service more capabilities, such as Direct Inward Dial (DID) numbers. The benefit of this service on the commercial level is the ability to avoid buying a PRI card (down the road--not right now in all cases) and just plug straight into the phone system.
Essentially, the power of PRI without the cost or limitations. SIP is only limited by your bandwidth, and carriers are coming up with some pretty interesting options.
This will be an area that many will need to become more familiar with, especially in the call center world.