What is the caloric theory of 18th century?

The caloric theory, developed in the 18th century, posited that heat is a fluid-like substance called "caloric" that flows between bodies and is conserved during transfer. According to this theory, caloric could not be created or destroyed, and it was thought to be responsible for thermal phenomena. This conceptualization helped explain heat transfer but was eventually replaced by the kinetic theory of heat and the laws of thermodynamics, which recognized heat as a form of energy rather than a fluid.