In the operant conditioning paradigm, extinction refers to the process of no longer providing the reinforcement that has been maintaining a behavior. Operant extinction differs from forgetting in that the latter refers to a decrease in the strength of a behavior over time when it has not been emitted.
Gel medium is an acrylic product. It comes in Heavy, Soft, and Regular and has a variety of finishes, Matte, Gloss and Semi-gloss. The basic use for these is to build texture in paintings by mixing them with acrylic paint. If you add a small bit of it to your paint it will also extend the drying time. The Soft gel is the medium that is most often used by paper artists. It can be used as a glue for collage and it is also used to make photocopy transfers.
Definition:  A gel is a sol in which the solid particles are meshed such that a rigid or semi-rigid mixture results. Examples: Fruit jelly is an example of a gel. Cooked and cooled gelatin is another example of a gel. The protein molecules of gelatin crosslink to form a soid mesh which contains pockets of liquid.