Trail renderer
A component that stretches a ribbon of geometry behind a moving object — sword swings, projectile arcs and light trails.
Unlike a particle system, which sprays independent points, a trail renderer builds one continuous ribbon mesh. Each frame adds a new pair of vertices along the object's path and drops the oldest after a set lifetime, so the ribbon follows the motion and fades behind it. The texture scrolls along the strip to suggest speed or glow.
Cheap and striking: a single sword swing or rocket tail reads clearly without hundreds of particles. The strip is usually turned to face the camera like a billboard so it shows from any angle. Unity and Unreal have shipped ready-made components for years.