Layer 7 Web gets its name from the seventh layer of the OSI model.  The OSI model (Open Systems Interconnected) is a conceptual model that contains seven layers. The layers are:

• Physical Layer
  • This layer “conveys the bit stream”. The physical means by which the data is transported. Wires, Cables, Optical Networks.
• Datalink Layer
  • This is where data packets are encoded and decoded into bits.
• Network Layer
  • Where the switching and routing for transmitting data from node to node.
• Transport Layer
  • Provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete data transfer.
• Session Layer
  • Establishes, manages and terminates connections between applications
• Presentation Layer
  • The presentation layer works to transform data into the form that the application layer can accept.
• Application Layer
  • Supports application and end-user processes

This is a great subject that is covered well in this Wikipedia.

~ Layer7web