Hi John, optics ready means the slide is cut to accept optics. Depending on the gun (and optic) , you may or may not need to purchase an adapter plate.
The P17 is RMSc Compatible, so the Holosun Multireticle will be a direct fit.
Stay safe & have a great day!

Hi John and welcome. Meaning = the Slide has been specifically designed for the addition of a Red Dot Optic. RMSc footprint Red Dots will mount direct to the slide. Visual and best Red Dot guide here: linkedin.com/pulse/best-red-dot-kel-tec-p17-shelly-jark-drakny-rmpkc ------------- Cheers, stay safe and enjoy!