Looks like a technical drawing board: small squares forming a nice grid.
Source We Are Pixel8
It’s okay to be square! A nice light gray pattern with random squares.
Source Waseem Dahman
Formed from a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Prismatic Abstract Background Design
Source GDJ
Derived from an image that was uploaded to Pixabay by darkmoon1968
Source Firkin
Based on several public domain drawings on Wikimedia Commons. This was formed from a rectangular tile. The tile can be accessed in Inkscape by selecting the rectangle and using shift-alt-i
Source Firkin
Same classic 45-degree pattern, dark version.
Source Luke McDonald
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
Not a flat you live inside, like in the UK – but a flat piece of cardboard.
Source Appleshadow
Colorful Floral Background 3 No Black
Source GDJ
Submitted in a cream color, but you know how I like it.
Source Devin Holmes
Could remind you a bit of those squares in Super Mario Bros, yeh?
Source Jeff Wall
Alternative colour scheme. Not a pattern for fabrics, but one produced from a jpg of a stack of fabric items that was posted on Pixabay. The tile that this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Lovely pattern with splattered vintage speckles.
Source David Pomfret
If you’re sick of the fancy 3D, grunge and noisy patterns, take a look at this flat 2D brick wall.
Source Listvetra
A light gray wall or floor (you decide) of concrete.
Source Atle Mo
Used the 6th circle pattern designed by Viscious-Speed to create a print that can be used for card making or scrapbooking. Save as a PDF file for the best printing option.
Source Lovinglf
A seamless pattern drawn originally in Paint.net by distorting a slice of background pattern 116 and copying the resulting triangle numerous times.
Source Firkin
Seamless pattern formed from a tile that can be extracted by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
Formed by distorting a JPG from PublicDomainPictures
Source Firkin
Very dark pattern with some noise and 45-degree lines.
Source Stefan Aleksić