SKIP is a term used to describe bending (or bouncing) of radio or TV signals in the ionoshpere... for TV usually layer E. But it happens only to HF and the lowest VHF channels, like 2 or 3. Above that the energy of the RF is too high to be "bent" back down to earth and passes off into space.

DUCTING or TEMPERATURE INVERSION is the physical phenomenon that brings us over the horizon TV signals. Warm days, then COOL and cloudless nights. This explanation itself is a generalization.