Other forms: grouting; grouted; grouts
Grout is a paste or putty that you use to fill in the spaces between tiles or along the edge of a tub. When grout dries, it keeps tiles in place, and once it's sealed, it protects against moisture.
An old-fashioned meaning of grout is "porridge or gruel," from the Old English gruta, "coarse meal," and a root meaning "to grind." These days you don't eat grout, but instead use it in home improvement projects, especially between floor or wall tiles. As a verb, to grout means "to apply grout."