The TCP/IP model competes with the OSI model as a layered architecture for networking.
See: RFC 1122
Sometimes the bottom two layers of TCP/IP model are combined, resulting in the following system:
The TCP/IP model is also called the Internet model. The TCP/IP protocols came first, and the model came later, as a description of the architecture of the TCP/IP protocols. This is contrast to the OSI reference model, which was developed as blueprint for a projected suite of OSI protocols.
In the most common usage, if layers are given by number, OSI layers are being referenced. However, if layers are named, TCP/IP names are often used. For example, the phrase "application layer" more often than not references applications in the TCP/IP way, encompassing the OSI session and presentation layers along with OSI layer 7.
References:
http://www.tcpipguide.com/free/t_TCPIPProtocols.htm
http://www.inetdaemon.com/tutorials/basic_concepts/network_models/TCP-IP_model/index.shtml