A measured amount of a solution of unknown concentration is added to a known volume of a second solution until the reaction between them is just complete; the concentration of the unknown solution (the titer) can then be calculated WordNet 3.0 & Open English WordNet

Titration is a common laboratory method of quantitative chemical analysis to determine the concentration of an identified analyte. Wikipedia

Common laboratory method of quantitative chemical analysis that is used to determine the unknown concentration of a known reactant. Wikipedia Disambiguation

The determination of the concentration of some substance in a solution by slowly adding measured amounts of some other substance (normally using a burette) until a reaction is shown to be complete, for instance by the colour change of an indicator. Wiktionary

Determination of concentration, by addition of reagent until completion of reaction. Wiktionary (translation)