I am not very clear about this
 

I am not very clear about this. I know base type and primitive type. But I haven't seen the physicalType in the source code.
For example, in the test case of kivaTest:

The boundary file:

piston
{
type wall;
physicalType movingWallFixedTemp;
nFaces 1326;
startFace 79522;
}

liner
{
type wall;
physicalType wallFixedTemp;
nFaces 2710;
startFace 80848;
}

where are these physicalTypes defined? And how they are used during computation?

The documentation is so brief on this.

physicalType is a concept we i
 

physicalType is a concept we introduced for FoamX and is not used by the rest of the code. It is the physical type of the boundary condition, i.e. the type which specifies the set of boundary conditions for all the variables e.g. inlet, outlet etc.

Explanation of boundary types:
 

Explanation of boundary types:
http://www.openfoam.org/doc/userse22.html