SPECIAL (MECHANICAL) EFFECTS VS. VISUAL EFFECTS
Special effects (often abbreviated as SFX, SPFX, F/X or simply FX) are illusions or visual tricks used in the theatre, film, television, video game and simulator industries to simulate the imagined events in a story or virtual world.
Special effects are traditionally divided into the categories of mechanical effects and optical effects. With the emergence of digital film-making a distinction between special effects and visual effects has grown, with the latter referring to digital post-production while "special effects" referring to mechanical and optical effects.
Wikipedia explains: https://en.wikipedia.org/wiki/Special_effect