Amnesia is loss of ability to memorise information and or to recall information stored in memory. What we call memory, the ability to recollect our life´s experiences, is a very complex process within the brain. Researchers are only beginning to understand what exactly happens when we commit something to memory or when we try to remember it.
Not all memories are permanent, so merely being a little forgetful is not the same as having amnesia. Amnesia is a large-scale loss of memories that otherwise would be unlikely to be forgotten, such as important life experiences and people, or things you have just been taught or told.
Amnesia is often the symptom of a degenerative brain disease, such as Alzheimer´s disease, or may result from a traumatic injury to the brain. There has been much debate over whether the brain "blocks out" particularly traumatic memories.