A choice that jumps ahead and skips content, usually awarding affinity in the process.
For example, when you visit the mall you usually get the option to visit several stores in the specific time period. A spur of the moment choice may be presented during a conversation, such as taking a girl to lunch or another activity. Selecting the impulsive option will, if accepted by the girl, progress to the next time period and automatically start the relevant scene.
In the above example you forfeit the chance to visit the other stores and whatever interactions they may have offered. However, you will usually be awarded a bonus of affinity points and the girl will remember the choice.
A choice is only classed as impulsive if another scene is skipped. Using the above lunch example, if the scene is the last in the time period then the lunch option is simply a regular choice. Thus no bonuses are awarded.