Ok i just had this question on a test and i never found the answer however i asked my teacher after i turned it in and he said they were refering to the object, the projection plane, and the line of projection, as well as 3rd angle projection- consisting of frontal plane, horizontal plane and the profile plane. it made sense untill he said the 3rd angle projection. idk i hope this helps someone get atleast closer to the answer

Thanks I have a test at ITT-Tech this Sat. and couldn' find a few of the things on the study guide.
Here are the others if you know them SECANT AND SCIENTIFIC DESIGN. AND THE RULE OF SKETCHING.