PTs and FYTs are at the core of the APWine protocol. Each with their own origin and meaning, they adhere to the ERC20 token standard - as such, can be freely transferred and traded.
Principal Tokens (PTs) (or APWIBT for APWine Interest Bearing Token) represent your locked position on a given Future. PTs are the proof of ownership of the assets you have deposited. They are not linked to any specific period, but rather to the Future itself - no matter when the deposit was made. When you want to withdraw your assets from APWine, you will need to burn these PTs.
Future Yield Tokens (FYTs) represent a right to claim the underlying yield of assets deposited in a Future. As opposed to PTs, they are uniquely associated to each period of a given Future. For instance, for a monthly Future, there may be an FYT for April, another for May, then June, and so on.
PTs and FYTs are always expressed in the same units as the underlying asset. This may not make a difference for a 1:1 asset such as aDAI / DAI, but comes into play when the underlying asset has a different value than the IBT, e.g. compounded assets. For instance, if you deposit 100 iFARM into APWine, with a price of 1 iFARM = 1.5 FARM, you will receive 150 PT, equivalent to a deposit of 150 FARM on APWine.