LOOGY (Left-handed One Out Guy) is a typical modern role for a left-handed relief pitcher, who comes in to face just one left-handed batter or two. The canonical example of a LOOGY was Jesse Orosco: for the last 13 years of his career, Orosco never averaged more than 1 inning pitched per appearance in any season, and in the last 5 years of his career he averaged less than 0.5 IP per appearance. Others who have had long careers performing this role include Mike Myers, Javier Lopez, Randy Choate, Trever Miller and Will Ohman. They will typically have a lot of appearances, few innings pitched, and very few decisions - wins, losses, or saves.
The term was coined by the staff of the on-line magazine Baseball Prospectus in the early 2000s, when the number of such pitchers proliferated. The term quickly gained wider popularity and is now commonly used throughout baseball. Tony LaRussa was known as a manager who was excessively fond of this type of pitcher, always keeping at least two and sometimes three in his team's bullpen, and making more in-inning pitching changes than any other manager.
Major League Baseball decided in 2019 to adopt a rule change, to come into forcve the following season, to curb the overuse of LOOGYs and the over-reliance on pitching changes in general, by decreeing a three-batters faced minimum for relief pitchers entering a game, barring injury or the end of the half-inning.