The term 'Piece of Solid Material' can be summarized by the crossword solution 'BAR', which is a three-letter word. A BAR is a solid piece of material, usually metal or wood, that is long and thin in shape. It is often used as a structural support in construction, such as for walls or ceilings, or as a barrier or railing. Bars are also commonly used in manufacturing, such as for reinforcing concrete or other materials.