Recognition (re+cognition) is a process that occurs in thinking when some event, process, pattern, or object recurs. Thus in order for something to be recognized, it must be familiar. This recurrence allows the recognizer to more properly react, survival value.
When the recognizer has correctly responded, this is a measure of understanding. For example, when some animals have never seen a human being before, they do not hide and they show no fear; but when they learn that a human being may be a threat, they may emit distress cries, flee or hide.
Even non-mammals can recognize when a situation signals danger, and will flee or hide. Baby spiders will flee when a mother spider sends a sharp pulse along the spider web. A male spider will gently poke a female spider's web to assess whether it is safe to approach the female without being killed himself.
In philosophy recognition became very important in Hegel's attempt at understanding the emergence of self-consciousness. Lack of recognition can also be attributed as alienation and it was this aspect of Hegel's work that Marx elaborated upon. The importance of recognition for Hegel is seen in his myth of the master-slave dialectic.