Final answer:
Internal energy refers to the sum of potential and kinetic energies in the particles of a substance, representing the total microscopic energy within a system.
Step-by-step explanation:
The type of energy that refers to the sum of potential and kinetic energies in the particles of a substance is known as internal energy. This concept is fundamental in the study of thermodynamics, where internal energy (U), sometimes symbolized as E, encompasses all the microscopic forms of energy within a system. The kinetic energy part is associated with the energy of motion of the particles, while the potential energy represents the stored energy due to interactions between particles or their position in a field.