Transfer: applies to physically transferring points between members and only one per use year allowed, in or out but not both.
Renting points: often what actually happens with a point rental is that the member rents by calling MS and, using his own points, makes a reservation in another's name. Calling it "renting points" is a convenient but somewhat inaccurate description of what actually occurs since what you are really doing is renting a reservation. Since no points actually transfer from the member to another, that is not a transfer subject to the one transfer per use year rule and you can do multiple such rentals per use year.
Banking: you can bank any or all of your points up until the end of the eighth month of your use year (and always count your beginning month as one when counting to eight). You can do as many banking events of some of your points as you want as long as all are done by end of that eighth month. If you use points and make a reservation and you cancel, you can then bank those points if you are still within the eight month banking period at time you cancel. If you cancel and you are beyond the banking window at time of cancellation those points have to be used by end of use year. Also, if you cancel 30 days or fewer out from date of arrival, points in reservation become holding points and cannot be banked, must be used by end of use year, and can only be used by calling to reserve 60 days or less out from date of arrival
Borrowing: you can borrow from a subsequent use year multiple times during a use year but you cannot borrow except when you are actually making a reservation for which you need to borrow points (and, if you think about it, you have absolutely no reason in the world to ever want to borrow when not making a reservation).
Transfers, banking and borrowing are final transactions; once done you can never send the points back to original owner in the case of a transfer, or to the original use year in the case of banking or borrowing. You cannot transfer to another member any banked or borrowed points, However, you can bank points that have already been transferred.