Kinktionary
More like guidelines and a lot less like definitions.
submissive
A person who agrees to submit or give up control in a relationship, scene, or activity.
Core BDSM
In Traditional BDSM/Core BDSM a submissive is someone who enters an Authority Transfer, therefore effectively and irrevocably transferring a negotiable portion of their agency to their Dominant. A submissive does not transfer ALL of their agency to their Dominant: for the parts not included in the AT there is no submission. Submission is a consensual process best negotiated at length before being entered into. Once the submissive consents to the Authority Transfer though, within the areas of submission they are not entitled to further right of consent and their only recourse to the will of their Dominant is to withdraw consent to the dynamic, therefore ending it.