140 BPM means 140 beats every minute: one beat every 0.43 seconds (429 ms), or 2.33 beats a second. In classical terms it is Allegro, fast and bright (120–155 BPM).
You often hear tempos around 140 BPM in rock, ska and country two-step, and trap felt at half this speed. The metronome above is already set to 140 BPM in 4/4: press Start, and change the time signature, accents, subdivisions or sound if your song needs it.