80 BPM means 80 beats every minute: one beat every 0.75 seconds (750 ms), or 1.33 beats a second. In classical terms it is Andante, at a walking pace (76–107 BPM).
You often hear tempos around 80 BPM in hip-hop, lo-fi, mid-tempo ballads and laid-back rock. The metronome above is already set to 80 BPM in 4/4: press Start, and change the time signature, accents, subdivisions or sound if your song needs it.