A slope jump is a jump done against a slanted wall or while walking up sloped ground which is used to gain more height than would be possible with a regular jump. The effect is amplified underwater without the Gravity Suit or Gravity Boost. It works because when Samus performs a jump, the game adds to Samus' existing vertical velocity. This means that if the player jumps while they are riding along a slope, they will gain more height than normal depending on the steepness of the slope. This has applications in many different places in speedruns, including to skip the Gravity Suit in Metroid Prime.
The two main ways you can apply this technique are with walls and with sloped floors. Using a wall, just hold L and walk near the given wall, then jump the moment before you run into it. With sloped floors, find the part of the floor in which it goes in an upward direction, then hold L and jump as you are in the process of moving up the slope.
This underwater slope jump in Tower of Light is an example of how slope jumps can be applied to a speedrun. Normally the game requires you to have the Gravity Suit, but by performing a slope jump, Samus is able to clear the height required to make it to the door.
The term "ghetto jump" was first used by kip on 9 February 2003 when he described that "a series of super ghetto jumps" could be used to climb Cargo Freight Lift to Deck Gamma in the crashed frigate without the aid of the Gravity Suit.
Many years later, many members of the community gravitated towards calling the trick "slope jump" instead, as it more accurately describes what the trick entails. The term ghetto jump is now considered to be archaic.