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.