It depends on the mass of the particle (total energy = rest energy + kinetic energy). For the purposes of the SRIM/TRIM examples, it’s only the kinetic energy that matters though.
Average energy needed to create an electron-ion pair in the gas.
It’s just to test that the algorithm used for sampling the number of electron/ion pairs for a given energy deposit does reproduce the requested W value and Fano factor. You can ignore it.