RBI scoring question

A question for the sages about this rule:

9.04 Runs Batted In

(a) The Official Scorer shall credit the batter with a run batted in for every run that scores

(1)  unaided by an error and as part of a play begun by the batter’s safe hit (including the batter’s home run), sacrifice bunt, sacrifice fly, infield out or fielder’s choice, unless Rule 9.04(b) applies

My question is about the term "infield out."

I mean, I know what the infield is. I know what an out is. I know what it means for an out to be made by infielders. But as far as my search has determined, there's no other reference to the term "infield out" elsewhere in the rules. Is this a reference to a specific circumstance resulting in an out in the infield? Or is this a general reference to, say, a routine 4-3 groundout? Or a bloop to short? Am I right in thinking that an "infield out" that brings a runner home is just a smaller-scale version of a sacrifice fly to the wall, in the sense that it, too, is a batted ball that scores a run even as it results in the batter being put out?

I don't think it's a reference to the Infield Fly rule, which is mentioned all over the place in the rules.