Many common substances around us exist as a solution, such as ocean water, air, and gasoline. All solutions are mixtures of substances that are composed of varying amounts of two or more types of atoms or molecules. A mixture with a non-uniform composition is a heterogeneous mixture, whereas a mixture with a uniform composition is a homogeneous mixture. The components that make the homogeneous mixture are evenly spread out and thoroughly mixed. 

A solution is a homogeneous mixture that is composed of a solvent and a solute. The solvent is present at a significantly greater concentration than the solute. The solute dissolves in the solvent, and the components distribute themselves randomly to form a solution.

The physical state of a solution — solid, liquid, or gas — is typically the same as that of the solvent. There are three main types of solutions; solid solutions, liquid solutions, and gaseous solutions. The solution phase is the same as the solvent phase. 

The solution consists of a mixture of separated solute particles (molecules, atoms, and/or ions), each closely surrounded by solvent species. The solvent and solute interact through attractive forces. This process is called solvation. When water is the solvent, the process is known as hydration. Due to solvation, the solute molecules remain dispersed throughout the solution. Solutions in which water is the solvent are called aqueous solutions. For example, ocean water is an aqueous solution of different salts dissolved in water. 

This text is adapted from OpenStax Chemistry 2e, Section 11.1: The Dissolution Process.