Kinktionary
More like guidelines and a lot less like definitions.
Cuckcake
A cuckcake is the femme presenting or identifying person outside a relationship that has sexual relations, scenes, and/or dynamic with one of the partners.
The cuckold or cuckquean can be subjected to implied or direct humiliation, degradation, and sadism by one or both of people involved in the scene or dynamic. This can cross over to romantic scenarios such as dates and going to public/private outings together.
The cuckcake can be submissive or a Switch to the person they are cucking with and Dominant to the person they are cucking. There are also Cuckcakes who are Dominant to both people in the couple.
There are no set rules on whether the cuckcake is a submissive, Switch, or Dominant to one or both people in the couple. They can have various designations if involved in a triad, throuple, or other polyamorous relationships/dynamic where they help cuck more than one partner.
Sometimes the cuckold or cuckquean is involved romantically, sexually, or platonically in the scene, relationship, and/or dynamic or scene with the cuckcake.