Right of First Refusal has a variety of applications. In this thread it was meant as the employer somehow getting the legal right to be the first entity to view any invention, idea, etc., and, if they refuse it, in writing, then the author/inventor/employer could take it elsewhere.

The employer would get to see everything before anyone else and reject what they didn't want. Normally they'd have to evaluate and reject such things within an agreed upon time frame.

hth