Short for Speed-Modification.
A Speedmod is a modifier in several music games like In The Groove, Beatmania, Dance Dance Revolution or O2Jam. A lot of Speedmods look like "x3" or "x 2.5".
Explaination:
When you play a song the notes of the songs will be displayed according to the BPM of the song (Beats per minute).
After you used a Speedmod the scrolling speed of the displayed notes will increase or decrease, but it won'
t change the BPM of the song.
Many players are using Speedmods to increase their playing
skill and timing.