From SmashWiki, the Super Smash Bros. wiki
A semi-spike or pseudo-spike is a type of attack that does not send the opponent directly downward, but instead in a mostly horizontal trajectory which (due to gravity) will quickly turn into a vertical trajectory. This is distinct from a meteor smash, which sends the enemy downwards without a prior horizontal trajectory. Semi-spikes are dangerous as they send targets on the shortest possible path to the blast line, and characters who survive are left below and away from the edge, the worst possible position to recover from. When landing semi-spikes on inclines, there will usually be little to no audible reaction from the character or the audience due to the fact that, like a meteor smash/spike landing on a grounded opponent, the character being hit cannot travel at an angle due to the incline. When grabbed characters are hit by other characters, they will be semi-spiked.
Lists of semi-spikes