Carpal Tunnel Syndrome is the name given to a condition where the nerve that travels through the wrist (the Median Nerve) is compressed. The tunnel in the wrist that the nerve travels through is called the Carpal Tunnel.
The nerve can be compressed by surrounding soft tissues (such as swollen tendons), a tight 'roof' to the tunnel (ligament or retinaculum), or a build up of pressure in the tunnel (fluid) due to hormone changes or other reasons.
When there is pressure on the nerve, messages can not travel along the nerve as normal. And this is what results in the symptoms associated with carpal tunnel syndrome.