backdoor

definition: a secret or underhand means of access (to a place or a position)
example:
speech part: noun
synonyms: back door
definition: an entrance at the rear of a building
example:
speech part: noun
synonyms: back door
definition: an undocumented way to get access to a computer system or the data it contains
example:
speech part: noun
synonyms: back door

How backdoor is being used?