This morning at the Winter Meetings, the Orioles selected two players from the Rule 5 draft; both of which are outfielders.
The rules for the Rule 5 draft can be somewhat complicated but thankfully, Fangraphs has a page dedicated to explaining the draft better than I ever could.
The Rule 5 Draft occurs in three phases, the MLB phase, where eligible players can be selected and placed on the 25-man roster for a $50,000 fee, and the Triple-A and Double-A phases, where players can be selected for a fee if they are not on the protected list, but in this phase, they do not need to go to the 25-man roster.