Taken from the game's official web page on Hasbro.com:

Bop It! is a brand that has built success on a simple concept: challenging your reaction time. Using a handheld game unit, players follow easy voice commands quickly and precisely, or they lose. It is straightforward and positively addictive! Bop It Smash takes the action one step further with moving lights, playing on an arcade theme that’s impossible to resist.

Time it right and smash the light! With BOP IT SMASH, colored lights in the center of the game unit fly back and forth while you do your best to capture one in the Zone. It’s active and fun – you and your friends will keep playing until you smash those lights every time!