Just the plain idea as “idea itself”, without application, without suggested use in an application.
An idea which solves a problem. But mostly the idea creators are just customers and not managers / politicians, so they are not able to change the world, at the source of the problem ( e.g. at the company which produces the product which might be improved,.. ).
In most cases, the idea creator has no “problem” that his/her idea is not implemented.... especially not he/she has no benefit if the idea is exploited... and so his/her intellectual property is just stolen.
The real problems of companies are such specific, that an ordinary owner of an idea can't solve, ususally.
Indeed, just browsing third-party ideas might help companies to solve problems. But as this browsing of ideas is adoption of ideas, this does not cause any payment duty - the reader of the third-party ideas just gets another idea, and thats the application idea which solves the application problem ( same applies to “benchmarking” of companies of different industries ).
The world is full of useful patents which are not used commercially by creating products & services.... and nobody cares about this .