Overwriting is a process of writing a binary set of data in computer data storage and is a term used to describe when new information replaces old information or data. In general it writes over the previous data, hence the name. Overwriting generally occurs when unused file system clusters are written upon with new data, though overwriting is also used in security algorithms. These algorithms use a precise set of rules to remove any part of an original data from the memory by writing a new raw data on the memory.
Data that has been overwritten, even just once, is generally considered to be unrecoverable. There have been theories regarding the feasibility of recovering overwritten data, but none have been put into actual practice. As such there is no evidence in favor of recovering overwritten data, but several suggesting it is entirely impossible.