The word decant means to pour or otherwise extract only liquid from a container that holds both liquid and solid particles. In chemistry, this term is often used in experiment instructions.
Though the word has applications in other areas (as wine connoisseurs will gladly tell you), in chemistry, decanting is the act of removing liquid from a container that contains both liquid and solid particles. There are a variety of methods for doing this, from simply pouring the liquid while being careful to leave the solids undisturbed to using a pipette or another extraction tool, which can be especially handy when volatile or otherwise dangerous chemicals are being used. Often, the solids left behind will be referred to as precipitate, which is a word that chemistry students may easily recognize from their classwork.