Energy is never created or destroyed, so the total energy stays the same in any system change. However, in every change some of the energy is transferred to the surroundings in ways that are not useful. We say this energy is dissipated. It ends up stored in less useful ways, mostly in the thermal store of the surroundings, where it is spread out and hard to use again.
Energy that is not usefully transferred is called wasted energy. It is not lost, but it is no longer helpful for the job we wanted.
There are many examples. A filament lamp transfers electrical energy to light, but most of it goes to the thermal store of the surroundings, which is wasted energy. A phone gets warm while charging. A car engine transfers energy from the chemical store of the fuel to the kinetic store of the car, but it also dissipates energy as thermal energy and sound. A bouncing ball rises to a lower height each time because some of its energy is dissipated as thermal energy and sound at every bounce.