1. A slave/submissive that completely devotes herself to her Master/Dominant, sacrificing her own desires and sometimes changing herself to mold herself into what her Master/Dominant requires of her.
2. A slave/submissive that has lost all personality in the process. When in a discussion, they readily cede, without giving any kind of input or putting up any kind of fight. They sound like Igor, saying "yes, Master" to everything.
There is a huge difference between 1 and 2. 1 is NOT a doormat. 1 is simply a slave that loves her Master and wants to please him. 2 is the real doormat. There is definitely a time when the slave needs to just accept her fate, and say "yes, Master," but there are plenty of times when a slave's input is desired and sometimes needed. Masters can't make decisions without knowing what's in the best interest of the slave. If the slave doesn't express her thoughts, feelings, desires, etc, how can the Master really claim to know his slave? How, then, can he make decisions that are best for the slave?
Basically, the doormat gives in all the time and buckles under any resistance from her Master. The non-doormat still retains her spunk, her identity, her inner fire, but knows when it's time to be respectful. It may be a fine art determining when to do be respectful and when to be feisty, but who said being a slave was easy?