Terms to know:
Source - The source is in reference to the x-ray tube. Specifically, it is the target within the tube when describing distances.
Image Receptor - The image receptor is the part of the system which accepts the x-rays to convert to an image. I can be the digital plate permanently within the table or wall bucky. It can be a computed radiography plate within the bucky or on the table top. It can be a film cassette within the bucky or on the table top.
Bucky - The image holder within the table or wall mounted system.
Object - Refers to the body part being imaged.
SID - Source to Image receptor Distance.
SOD - Source to Object Distance.
OID - Object to Image receptor Distance.
Central Ray - Refers to the primary beam, specifically the exact center of the primary beam
Distortion - There are 2 types. Size distortion, and shape distortion.
Size distortion - Magnification. When the size of the object being imaged is not truly represented in size.
Shape distortion - there are 2 types of shape distortion. The result of the shape distortion depends on how the image receptor, object, and central ray are positioned.