Doppler effect: alteration in the observed frequency of a sound due to motion of either the source or the observer.
Doppler shift: the actual change in frequency due to the relative motion of source and observer.

Definition found in OpenStax University Physics. Authored by: OpenStax CNX. Located at: https://cnx.org/contents/1Q9uMg_a@10.16:Gofkr9Oy@15. License: CC BY: Attribution. 

• Roche Limit: the distance from a planet's center within which a satellite can neither approach nor reside without being disrupted by tidal forces (Merriam-Webster)
• Tidal Force: difference between the gravitational force at the center of a body and that at any other location on the body; the tidal force stretches the body (University Physics Volume 1)