100 BPM means 100 beats every minute: one beat every 0.6 seconds (600 ms), or 1.67 beats a second. In classical terms it is Andante, at a walking pace (76–107 BPM).
You often hear tempos around 100 BPM in pop, funk, soft rock and filmi dholak grooves. The metronome above is already set to 100 BPM in 4/4: press Start, and change the time signature, accents, subdivisions or sound if your song needs it.