“AiO” stands for “All-in-One” and means the pad has all the absorbency materials sewn in, and is simply placed into your underpants as-is, like you would use a disposable pad. These pads contain no synthetic leakproofing materials, and are more “natural”.
Click the image of the product to see the full information page for that product.
The pad listings include letters in brackets to tell you the absorbency and waterproofing.
“L” = Light. “R” = Regular. “H” = Heavy.