It refers to sensor size in DSLR. Full frame means the sensor is the same size as 1 frame of your normal 135 format (35mm) film (36X24mm). 1.3 crop means that the sensor is about 77% of the full frame size. The implications of the crop factor is many, one of which is the angle of view. Crop size sensors (APS H=1.3, APS C=1.6/1.5) tend to use a percentage in the center of the image circle of lenses, and so your 18mm wide angle on a 1.3 crop becomes a less wide 1.3X18=23.4mm and on a 1.6/1.5 crop (most consumer to prosumer level DSLRs) body becomes a 1.6X18=28.8mm lense. Also there is the very important issue of sensor noise. Full frame sensors tend to have larger photosites and thus generate lower signal to noise ratio (to over simplify). A full frame sensor versus a cropped sensor, both 12 megapixels for example, will more likely deliver (the full frame) a less noisy image compared to the cropped sensor.
http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm