means The curved path an object follows as it moves through space, especially under the influence of forces like gravity — or, by extension, the course of anything developing over time.

from From Latin trajectus, the past participle of traicere, 'to throw across,' built from trans- ('across') plus jacere ('to throw') — the same jacere that launches words like 'project' and 'eject.' So a trajectory is literally the line traced by something thrown across space, a notion that took mathematical flight in the 17th century as scientists started plotting where hurled and falling things actually go.