Bedikas Chametz, or Bedikat Chametz, is the search before the Jewish Holiday of Pesach for Chametz. The search takes place after nightfall on the evening before Pesach (the night of the 14th of the Hebrew month of Nisan, as stated in the Mishnah tractate Pesachim). When Pesach starts on Saturday night, Bedikas Chametz takes place on Thursday night (two nights before Pesach).
The lights around the house are turned off, and a candle is lit. A blessing is recited if the search is performed on the 14th (or on the 13th when the 14th is on a Friday), but not when an earlier search is performed for various reasons.
In order to prevent the possibility of making a blessing in vain (which might occur if there was no chance of finding chametz in the house), and additionally to keep children interested and involved, there is a widespread custom to 'seed' the area to be searched. Prior to Bedikas Chametz, several (usually ten) pieces of chametz are hidden around the house, preferably by a child if available. These pieces must be small and should be wrapped so that crumbs do not escape.
Traditionally, a feather and a wooden spoon are used, and whenever a piece of chametz is found (whether one of the hidden pieces or another that is discovered unexpectedly), the feather is used to sweep the piece of chametz into the wooden spoon, which is then used to place it in a bag. It is best to use a candle to illuminate the areas; however, it is perfectly acceptable to use a flashlight or other light source.
Every part of every room of the house where chametz may possibly be found must be searched using this process. Rooms where chametz is not normally brought (such as a bathroom) need not be searched.
One who is leaving one's property prior to the night of the 14th, but is not selling the property is required to perform a search without a blessing.