From NENA Knowledge Base

Femtocell is a residential or business customer small cell that generally has a radius range of approximately 10 meters (or approximately 33 feet), that generally requires the customer to have a wired broadband connection in order for the wireless carrier to activate and register the small cell for use and connect the call to the mobile switching center, and that enables the customer to move the small cell and re-register the small cell.

Relevant NENA Documents

NENA-INF-018, NENA Non-Mobile Wireless Service Interaction Information Document