Looks like a technical drawing board: small squares forming a nice grid.
Source We Are Pixel8
Snap! It’s a pattern, and it’s not grayscale! Of course you can always change the color in Photoshop.
Source Atle Mo
Adapted heavily from a JPG that was uploaded to Pixabay by Viscious-Speed.
Source Firkin
A seamlessly tileable pink background texture.
Source V. Hartikainen
A pattern derived from part of a fractal rendering in Paint.net.
Source Firkin
A repeatable image with dark background and metal grid pattern.
Source V. Hartikainen
Not even 1kb, but very stylish. Gray thin lines.
Source Struck Axiom
Clean and crisp lines all over the place. Wrap it up with this one.
Source Dax Kieran
Pixel by pixel, sharp and clean. Very light pattern with clear lines.
Source M.Ashok
Just the symbols of the signs of the zodiac distributed in a chequer board-like pattern
Source Firkin
Seamless Olive Green Web Background Image
Source V. Hartikainen
Remixed from a raster on Pixabay, that was uploaded by ArtsyBee.
Source Firkin
Don’t look at this one too long if you’re high on something.
Source Luuk van Baars
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
A slightly more textured pattern, medium gray. A bit like a potato sack?
Source Bilal Ketab
A monochrome pattern from a tile that can be had by selecting the rectangle in Inkscaope and using shift+alt+i
Source Firkin