or may abe  direct  me  to where  I can get this info

A quick internet lookup would have releaved your answer:

Retail Display Allowance (RDA) is a fee paid by publishers to qualifying retailers as an incentive for displaying that publisher’s title(s) in its store(s) and to increase sales through better visibility and positioning.

Retail Display Payment (RDP) is sometimes paid instead of RDA. RDP is another form of payment for some checkout titles only.

IPO = Initial Pocket Offerings