Wikipedia has several pictures of MOSFETs and various types of them. Here is one.
Notice that the Source and Body are connected. I understand this is to ensure there is no forward-bias or reverse-bias between them.
What I don't understand is, what is that "P+" region where the body connection exists? What is it and what is it's purpose? If it's a more highly-doped p-region then I don't understand why.
In a semiconductor, you can't generally make a resistive (ohmic) contact to a lightly doped region (as in the p substrate or bulk here). Such a contact would likely be very resistive, or act as a Schottky diode.
So (just like the N+ in the drain), a very heavy P+ diffusion is made for the metallic contact. This creates a degenerate (i.e. metallic or conductive) junction between the metal and the semiconductor, thus giving a good electrical contact to the bulk.
A secondary advantage of this is that the P+ bulk and N+ source can be quite close together. Having a low resistance connecting shorting these makes the FET more robust during high VDS voltages.
