"A horse that stood in front of the house."
Translation:집앞에 선 말.
I was taught that 서다 is "to get into standing position - > to stand up, to stop (while walking)", and that "to be standing" is 서있다. Unless that was misinformation, wouldn't that make 집앞에서 선 말 "a/the horse which stood up/stopped in front of the house"? If so I would actually recommend removing this phrase for this lesson because verbs like 서다, 앉다, 눕다 etc. need some explanation in and of themselves (maybe in a dedicated skill?) and the past participle of 서있다 is 서있던 which is probably a bit too advanced at this point.