The shutter speed is a measure of how long how film or sensor is exposed to light, due to the shutter being opened and closed. This is usually measured in seconds, or fractions of a second. Longer shutter speeds allow more light to onto the film or sensor and allow more subject movement.
Tonight while shooting a show I noticed that with each shutter release the shutter speed would change like it was bracketing for some reason. I don't know how or why it started but I need to get it ...