Clarification on Backdoors

I had a quick question on backdoors that I wanted to clarify on. Your lesson on them gave quite a bit of good info but I just need some clarification. Are Backdoors a type of malware that utilize bugs in systems to get into your system. or are they more like the name suggests that it is a virus that allows other viruses to get into your system without going through the security measures?

A backdoor is a loaded term that is used loosely by the media to mean many types of security problems. But in a more traditional definition it is usually a secret method of bypassing access control into a system. A virus or malware can create a backdoor. But also a configuration change can create a backdoor such as the example of the weakening of the random number generator, based on the NSA’s Dual_EC_DRBG algorithm. A backdoor can be deliberate or accidental. They can be specifically coded into something or even used by the owner to gain access to their own systems like with port knocking.