Reconsolidation is the action of reactivating existing memories from the past. Initially memory consists of the consolidation of information absorbed by the senses. Reconsolidation refers to the retrieval of memories in response to a memory trace. This is how and why we can recover memories from long ago or about topics that you haven't thought about in a long time.
As an example, a child learns a language while growing up. The child is then adopted into a family that speaks a different language. The child then learns to speak their family's language. Then several years later the older child or adult is exposed to their first language again. The adult will be able recall that first language and start using it again with only a minimum of difficulty. Or, even simpler, a child learns to ride a bike or to roller skate. That child grows up and doesn't do either of these things for several years but given the opportunity they would still remember how to bike ride or skate.