Drainage basin
an area of land that is drained by a river and its tributaries
watershed
a geographical area of land that compromises a set of rivers and streams that drain into a central body of water
confluence
a point in which 2 rivers meet
tributary
a small river or stream that joins a large river
Source
the starting point of a river
mouth
a point in which a river enters a sea
estuary
Where river water meets sea water and mixes