The anacronyms vary
TF (trade or time for photos)
TFP (trade or time for portfolio)
Paid - usually for currency.
PT (part trade, part something else)
They can vary in the industry.
TF is Trade or Time For (whatever you both agree on)
TFP is traditionally Trade For Prints (Not used as much any more)
TFCD is Trade For images on a CD
Paid shooting for money - Typically will not also include images for you to use.