Sample separation using chromatography is based on the use of two different phases:
Mobile phase: This is the phase the sample is mixed with. It allows the sample passing through the stationary phase and the whole system. Mobile phase normally defines the type of chromatography.
Stationary phase: This phase can be packed in a container called column, or be on a surface. This phase does not move, hence its name. Molecules with greater affinity to this phase will elute later.