In chromatography an eluent is the liquid or gas entering a chromatographic bed (e.g. a column) used to effect a separation by "elution". The "eluate" is what comes out of the chromatographic bed for collection. The elution time is the time required for an analyte to exit the system.

An often related term is "mobile phase." In chromatography, the mobile phase consists of the sample being separated or analyzed and the solvent that moves the sample through the column. In contrast, the eluent, is just that solvent.