What do two or more substances form when they come together without forming a new substance?

Two or more substances when come together without forming a new substance form a mixture.

For example, when you add salt to water, they do not form a different substance, they form a solution where the salt dissolves in water. A solution is an homogeneous mixture.

Other example, when you mix salt and sugar, they do not form a new substance, but an heterogeneous mixture.