A language parent is essentially someone (a KZbinr for example) that you exclusively use to get all your comprehensible input from. So any videos you're watching (what's in my bag, a day in my life, let's plays, etc) would come from that one person. You'd then begin picking up their speech mannerisms. Originally when referring to a language parent, if lets say one of your parents speaks a foreign language while the other speaks your primary language, you'd prolly get all your experience and mannerisms in the foreign language by listening to how that parent speaks. Hope this makes sense!