Chromatography is a technique used to separate the various components in a complex mixture or solution. There are two parts: a stationary phase and a mobile phase. The stationary phase does not move. It is the platform on which you put the mixture you want to analyze on. The mobile phase does exactly what you would expect given the name — it moves. It sweeps the components in the mixture along the stationary phase separating them by how much they "stick" to each other. It is also referred to as the solvent.