backdoor vs back entrance

backdoor and back entrance both are nouns.

Word	Noun	Adjective	Verb	Adverb
backdoor	Yes	No	No	No
back entrance	Yes	No	No	No

As nouns, backdoor and back entrance are synonyms defined as:

Other synonyms of backdoor include back door.

backdoor (noun)	back entrance (noun)
a secret or underhand means of access (to a place or a position)	an entrance at the rear of a building
an entrance at the rear of a building
an undocumented way to get access to a computer system or the data it contains