Solid-phase refers to a state of matter where particles are closely packed together, resulting in a fixed shape and volume. In this state, the molecules vibrate but do not move freely, which gives solids their rigidity. Common examples of solid-phase materials include metals, ice, and wood. In various scientific fields, solid-phase processes are important. For instance, in solid-phase extraction, a solid material is used to separate compounds from a mixture. Additionally, in solid-phase synthesis, chemical reactions occur on solid supports, facilitating the production of complex molecules, such as in the development of pharmaceuticals.