1. A letter of the Greek alphabet.
2. An area, positioned at the end of a river (adjacent to an ocean, sea or lake), comprising of the silt brought by the currents of the river and deposited as the water lost its initial speed. The area is characterised by the river dividing in a number of streams, often leading to a maze of streams dividing and coming together.
The most famous delta is that of the Nile, and it is this delta from which the term is derived, because the Nile delta has a very characteristic triangular shape, which the letter delta has as well. Other rivers with notable deltas include the Ganges/Brahmaputra combination (spanning most of Bangladesh), the Niger, the Amazon, the Mississippi and the Rhine.