Answer
A reaction which involves the formation of an insoluble solid is called precipitation reaction.
Work Step by Step
A reaction in which two soluble salts react in order to yield an insoluble solid, called a precipitate (which settles at the bottom of the test tube) is called a precipitation reaction.
Example- $AgNO_{3}$ $+$ $KCl$ $=$ $AgCl$ $+$ $KNO_{3}$.
Here AgCl forms a precipitate and settles down.
