The dropping of eroded particles as sediments, commonly in layers.
In geology, the process of deposition of a solid material from a state of suspension or solution in a fluid (usually air or water). Broadly defined it also includes deposits from glacial ice and materials collected under the effect of gravity alone, as in talus deposits, or accumulations of rock debris at the base of cliffs.
Definition adapted from Answers.com.
For more, visit the Wikipedia entry for deposition, URL: http://en.wikipedia.org/wiki/Deposition_(sediment)