Go inside and play a little with the custom block! A terp is when the sprite goes fast and then slows down when it comes to it's final position. I just made a custom block to make it easier to use. Remember to put the define block in your backpack, and not the actual block. You don't need to use credit, but it would be nice if you did ;)
Feel free to use! Credit goes to @MathMathMath for their amazing gliding tutorial. They have tons of awesome tutorials, so you should go check them out.