A "screen door", if I understand the parlance correctly, is some kind of fine-mesh door that is put into a doorframe to prevent insects from getting in.
How it relates to VR is, when you look at a typical LCD display from up-close, magnified, you start noticing the elements that make up the picture, which makes the image look as if you're looking at it through a fine mesh - hence, "screen door effect".
Okay. Yes, I understand. Thanks.