DEP stands for Drive Enhancement Proposal.
A DEP is a design document providing information to the Drive community, or describing a new feature for Drive or its processes or environment.
The DEP should provide a concise technical specification of the feature and a rationale for the feature.
The gaol of that ticket is to create the skeleton for such document that will be stored in https://github.com/nuxeo/nuxeo-drive/tree/master/docs/dep.