Ok, I’ve never heard it referred to as such. If you look at the photos on the pattern listing you can see how much space is designed in the front. One of the photos shows the shirt buttoned up to the very top. I don’t have a shirt to check the space and don’t recall off the top of my head, but it could be as much as an inch.
https://oliverands.com/shop/buttoned-up-button-down-shirt-sewing-pattern.html
If yours is looking like this you should have it right. Be sure that when you sew the collar you’re matching the ends of the collar to the dots on the collar band pattern piece and then you should be sewing it correctly. You could certainly lengthen the collar a bit at the center and close up the space if you aren’t happy with that amount of space. I hope that helps.