Fully diluted capitalization counts not just issued shares but everything that could become shares: granted and ungranted option pool, warrants, convertible notes and SAFEs on an as-converted basis. It is the denominator that matters for ownership and price-per-share math.
Investors price rounds and calculate ownership on a fully diluted basis so future dilution from the pool and convertibles is accounted for upfront — which is why topping up the option pool pre-money effectively dilutes founders rather than new investors.