If you fire rockets at closest approach to get more delta-V, that's an Oberth Maneuver - https://en.wikipedia.org/wiki/Oberth_effect https://en.wikipedia.org/wi

If you fire rockets at closest approach to get more delta-V, that's an Oberth Maneuver - https://en.wikipedia.org/wiki/Oberth_effect https://en.wikipedia.org/wiki/Oberth_effect And as you say, an unpowered planetary flyby is a gravity assist.