A precipitate is a solid that is formed as a result of a chemical reaction.
For example, if you combine 2 liquids and get a solid in the resulting solution, the solid is your precipitate.
An example of a reaction could be:
2AgNO3 + ZnCl2 -> 2AgCl (s) + Zn(NO3)2
AgCl is a common precipitate in reactions - it is found as a solid.