Changed your equalizer profile
Prevented songs from skipping
Shuffled your playlist
Protected against electrostatic shock
Correct Answer: Prevented songs from skipping

A brief explanation why…

First appearing in the mid-90s, the ESP (Electronic Skip Protection or Electronic Shock Protection) button enabled a data buffering feature on portable CD players to help prevent audio playback from skipping when the device would experience physical shock such as being in your pocket during a jog.

When activated, audio would be stored in RAM before being piped through the digital-to-analog converter, giving the CD player time to find where it left off reading and allowing playback to continue when it would otherwise skip.

Early on, the feature could only buffer about three seconds and naturally faded out of necessity amid the rise of flash-based MP3 players.