A flow field assigns every point in space a direction, and things moving through it follow the local arrows. Fill the field with smooth noise and particles trace wind-blown paths; animate the noise and the whole space breathes.
The technique is generative art’s favorite shortcut to organic motion because it decouples the choreography (the field) from the performers (the particles). One field change redirects a hundred thousand elements coherently.
True fluid simulation computes physics; a flow field just declares motion. The declared kind is cheaper and art-directable, which is why so much living, drifting imagery on stages is noise-driven fields under particles.