ground floor
noun /ˌɡraʊnd ˈflɔː(r)/
  /ˌɡraʊnd ˈflɔːr/
 (British English) (North American English first floor)
Idioms - the floor of a building that is at the same level as the ground outside
- a ground-floor window
 - I live on the ground floor.
 
 
Idioms 
be/get in on the ground floor 
- to become involved in a plan, project, etc. at the beginning