A backdoor is about any method by which user is able to get around regular security measures and get high level access type on a system/app. Backdoor Trojans couldn’t be more appropriately named as they offer the person or group who created them the ability to slip unnoticed into the victim’s machine and make changes to it both remotely and invisibly. If a user’s machine becomes infected with a backdoor, then they probably won’t even know it’s there. It may only be later that they find out that a backdoor can be used to do things like run malware, remove private information, or send login details to external sources.
Please note that technologies described on Wiki pages are not necessary the part of Plesk control panel or its extensions.