The removal of personnel or units from area under enemy control. The removal of personnel or units from areas under enemy control by stealth, deception, surprise, or clandestine means.
Exfiltration is also a term used by civil engineers. It is method for managing storm water runoff.
In computer terms, Exfiltration refers to the unauthorized release of data from within a computer system. This includes copying the data out through covert network channels or the copying of data to unauthorized media.