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.
I've decided to get back to using my Holga, and while in the past I've been happy with the the pics I have taken, I started thinking about how "accurate" the settings on the camera are. (Yes I know ...