A rootkit is a different beast. A backdoor is simply a (covert) way to gain remote access to a system. A rootkit involves being able to elevate user permissions such that you have full control over the computer. Rootkits also typically use such permissions to hide themselves from normal user accounts.
I guess in a way you could see them as related, in that they both are access tools. A backdoor gets you remote access to the system in the first place. A rootkit gets you elevated access after you are in the system.
I guess in a way you could see them as related, in that they both are access tools. A backdoor gets you remote access to the system in the first place. A rootkit gets you elevated access after you are in the system.