Crop frame/factor is basically the diagonal ratio of 35mm of the image sensor's frame. Sometimes referred to as the focal length multiplier. Therefore if say you are using a 50mm lens, the crop factor will increase your max focal range of your lens on the image sensor.
On the other hand, full frame is when your image sensor is as big as a 35mm film format. You will notice that this will maximize your images on cameras that have image sensors like this.