What does it mean to titrate a solution?

Titrating a solution involves adding a solution of known concentration (titrant) drop by drop into a solution of unknown concentration (titrand). This is done using a calibrated burette. The endpoint of titration is determined by a color change or an electrical measurement. When the titration reaches its endpoint, the volume of titrant used is measured. This measurement allows researchers to calculate the concentration of the titrand. 

Titration is widely used to test the purity of synthesized pharmaceuticals and other chemical compounds.