I always get 'em confused but it's the "H" vs "Y" - both TEs, one more "traditional"/physical, one more athletic/fast/quick/hands.
What makes Gronk such a freak is that he has more hands/athleticism that the typical "traditional" TE.
And if you can put both H and Y on the field at the same time and add in a legit outside WR, it's a matchup nightmare for opposing defenses.
Yeah, IDK on the letter designations could even be different depending on OC I've always referred to them as "in line" or "move" or if you prefer
Gruden- speak "move" becomes "joker".