A solidus (the Latin word for solid) was originally a gold coin issued by the Romans. It was introduced by Constantine I in 309–10, and was used through the Byzantine Empire until the 10th century. The coin replaced the aureus as the main gold coin of the Roman Empire.

The diagonal stroke (slant line) that is often used to show rates, when units are expressed in abbreviated or symbolic form (i.e., km/h).

The solidus character U+2044, ⁄, also known as a shilling mark, is a punctuation mark. The character found on standard keyboards is the virgule (commonly called forward slash).

The highest temperature at which a metal or an alloy is completely solid.

Temperature at which freezing is completed. Below that temperature all metals are completely solid.

The temperature at which some components of the solder alloy begin to melt. See liquidus and pasty range.

In chemistry, materials science, and physics, the solidus is a line on a phase diagram below which a given substance is stable in the solid phase. Most commonly, this line represents a transition temperature. The solidus may be a straight line, or it may be curved, depending upon the substance.