Tributary     -   A smaller stream which joins a larger stream or river.

River System   -   The main river and its tributaries.

Sources       -    The point where a river/tributary begins.

Mouth          -    The point where a river/tributary ends (lake/sea).

Course         -    The path that a river/tributary flows from source to the mouth.

Long profile     -   The plot of height along the river/tributary.

Cross-section   -   The plot of height across the river/tributary.

Load - The materials carried by a river/tributary (rocks, pebbles, sand, silt, clay).

Drainage System   -    The area drained by the main river and its tributaries, bounded by a divide or watershed. It is also called a catchment area.

Alluvium     -   The materials composed of clay, silt and sand deposited by a river/tributary.

Drainage density   -   The average length of the stream per unit area. Rainy areas and areas with impermeable rocks have a higher drainage density than arid regions and those with with permeable rocks.