Procedural memory is a memory of skills and procedures. As compared with declarative memory, it is governed by different mechanisms and different brain circuits. An example of procedural learning is learning to ride a bike, learning to touch-type, learning to swim, etc. There is no simple stimulus-response pairing. Instead, the brain is trying to figure out optimum memory pattern by trial and error. Procedural memory can be very durable.
Studies of people with brain injuries suggest that procedural memory and episodic memory use different parts of the brain, and can work independently. For example, some patients are repeatedly trained in a task and remember previous training, but don't improve in a task (functioning declarative memory, damaged procedural memory.) Other patients put through the same training can't recall having been through the experiment, but their performance in the task improvess (functioning procedural memory, damagec declarative memroy).