I think that as with many things in cycling, there really is no standard here. There is no internationally recognised accreditation stamp that a manufacturer can put on their product to say 'actually, really, tubeless ready'. You have these 'TR' marks on stuff but it really means nothing.
A 'tubeless ready' tire is pretty clear - it's a tire that you can use either with or without an inner tube.
A 'tubeless ready' wheel is in my opinion a grey area. Is it a wheel that can go tubeless without any modifications? Is it a wheel that 'just' needs a basic conversion? With different levels of conversion almost any wheel can go tubeless so what's the point of calling it 'tubeless ready' in the first place? Maybe it's a wheel where you can apply mods and still retain warranty? Who knows?