To gently pack down the burning tobacco in a lit pipe. Doing so keeps the smoldering tobacco in contact with the unlit tobacco, keeping your pipe from going out.
A tamper is a hand-held device with a flat or convex base used during the preparation of a shot of espresso to compress ground coffee into a puck, within the portafilter's basket. Tampers vary in weight, diameter, and design. Generally, the diameter should match that of the basket, and the weight of ornamental designs is of personal preference.
In blasting, to plug up with clay, earth, dry sand, sod, or other material, as a hole bored in a rock, in order to prevent the force of the explosion from being misdirected.