Soluble - The term soluble means that a substance dissolves. 
An aqueous solution is soluble.  If one mixes two solutions together and no precipitate forms, then only the ions are
in solution.  Thus, there is no reaction.

Note:  Sometimes two solutions are mixed together,  a reaction
can occur that does not form a precipitate.  Usually when this type of reaction takes place, there is a marked
color change when the product is formed or a large
temperature change is observed.

Insoluble - The term insoluble means a
substance does not dissolve. 

Precipitate – A solid beneath a liquid.  If one
mixes two solutions and a solid forms,
this is called a precipitation reaction.