They are the hydraulic lift points on the back of the tractor, you attach an implement to it (like a grader blade or a ripper etc) & you can raise & lower it with a control lever.
Poor silly old Buni had a grader blade on it that he left on the ground & then tried to reverse over it… Nnnnnnnnnnnnnnnnnnnuh, not going anywhere.
Had to move a large log out of the carport but couldn’t get the 4 in 1 over it and had to roll it so I could get a grip on it, put the bucket on the log and applied some down pressure and reversed.
Started to roll over then the tractor fell off the log sideways denting the fender on my new car with the bucket.
A little pissed off to say the least.