Withbeing committed every "property" on an entity is called a "field" now. Once everything is converted to use that, most code should rely just upon the Entity Field API. However, still some code will have to work specifically with field.module fields, i.e. fields that can be configured via the UI (and so extend the entity).
Some suggestions for this were:
- configurable field
- dynamic field
Fields defined by the entity type are right now called "base fields", other suggestions were
Also, the 'fieldable' key in hook_entity_info() could be need renaming. E.g. to 'extendable' or 'configurable'.