What term describes a dissolved molecule or ion in a solution?

The term that describes a dissolved molecule or ion in a solution is "solute." In the context of solutions, a solute refers to the substance that is present in a lesser amount and is dissolved by the solvent, which is the substance that makes up the majority of the solution. For example, when table salt is dissolved in water, the salt is the solute, while the water is the solvent.

This distinction is crucial in understanding how solutions are formed and the roles different substances play in the process. Solvation involves the interaction between solute and solvent, which helps in the dissolution process but does not specifically define the solute itself. While "species" can refer to any type of chemical entity, including molecules or ions, it’s a broader term that doesn’t specifically denote the dissolved nature of the entity in solution.