Last week, the Rockies outrighted four players off their 40-man roster: Brooks Brown, Simon Castro, Gonzalez Germen, and Michael McKenry. They did this because they needed to clear space on their overcrowded player catalog (more on this in a moment).
When a player is outrighted, it means their name is immediately removed from the 40 man roster. From there, they have to pass through waivers in which the other 29 teams get a shot to acquire them. Then, if they're not claimed by another team through that process, they can then be sent to the minors without taking up space on the 40-man roster.