A stream or part of a stream that flows only in direct response to precipitation; it receives little or no water from springs, melting snow, or other sources; its channel is at all times above the water table.
http://www.floodcontrol.co.riverside.ca.us/content/glossary.htm
A stream that only flows right after a rain. These streams may only flow for a short time in any year, yet they support more vegetation than surrounding drier areas.
http://www.pima.gov/cmo/sdcp/kids/gloss.html
A watercourse generally without a well-defined channel which flows only in response to rainfall or snowmelt. Ephemeral streams flow for less than 20% of the year during normal rainfall conditions.
http://www.state.sc.us/forest/rbg.htm
a water conveyance which lacks substrates associated with flowing waters and flows only in direct response to precipitation in the immediate watershed or in response to melting snowpack and which is always above the local water table.
http://www.dep.state.pa.us/dep/subject/advcoun/wetmgt/definitions.htm