Spinal nerves become symptomatic and produce pain when they are compressed. Most commonly, a disc prolapse will push the nerve against an overlying bony structure.
A microdiscectomy describes the procedure where the offending small portion of the prolapsed disc is removed using magnification and a unilateral (one sided) approach.
The foramen refers to the tunnel through which the spinal nerves exit the spinal canal. When the nerve is compressed here, part of the tunnel is opened up to relieve the nerve. This is called a foraminotomy.