Screen Door Effect
Screen door effect is the term that refers to visible fine lines between pixels on a display, as if you're looking out of a screen door.
Though once common with LCD and DLP projectors, it is now fairly rare thanks to increased quality of the imaging chips, and higher resolutions. LCOS projectors like SXRD and D-ILA had pixels close enough together to have rarely had this issue.
With inexpensive, lower-resolution projectors, this effect is still possible. The only way to make it less visible, is to reduce the size of the image.