It doesn't seem like there is consistency in the way posters define stretch 4. Not sure I agree with their definitions either.
See link for one sites definitions of Off-the-Ball Combo Forward and The Scoring Combo-Forward
The Stretch 4
The stretch 4 is generally a one-dimensional player, varying based on athleticism. The key to this position is the ability to knock down "catch and shoot" three-pointers, hence the word "stretch", as in stretching the defense and spreading the floor.
A stretch 4 is really a 3, yet has the size to draw opposing power forward defenders away from the rim, keeping them out of their comfort zone while diminishing their presence in the paint.... by simply stretching the floor, catching and shooting. It's a player-type that lacks strength, making it difficult to convert contested shots inside and defend true power forwards.