Definition
Open scope is the design choice in RoHS that makes the rule cover everything by default. Since the 2011 recast became fully open in 2019, RoHS reaches all electrical and electronic equipment unless a specific category is carved out, rather than naming the handful of categories it applies to.
The difference is in where the burden sits. A closed list says "these categories are covered, and nothing else." Open scope says "everything is covered, except these." That flips the default, so a product is presumed in scope and the maker has to point to an exclusion to get out.
For RoHS the practical exclusions include things like large fixed industrial tools, certain means of transport and active implantable medical devices. Everything else that fits the EEE definition is in, even equipment that was never on the original category list.
With open scope, "my product was not on the list" is not a defence. If it is EEE and no exclusion applies, RoHS applies.
Note: general educational information, not legal advice. Check the official source before relying on it.