What is the internal energy of a system?

(N/A) The internal energy of a system is the sum of all microscopic forms of energy present within the system.
It includes the kinetic energy of the molecules due to their random motion (translational,rotational,and vibrational) and the potential energy associated with the intermolecular forces and the structure of the molecules.
Internal energy is a state function,meaning it depends only on the current state of the system (defined by variables like pressure,volume,and temperature) and not on the path taken to reach that state.
It is denoted by the symbol $U$.