Looks like a technical drawing board: small squares forming a nice grid.
Source We Are Pixel8
This is so subtle you need to bring your magnifier!
Source Carlos Valdez
Medium gray pattern with small strokes to give a weave effect.
Source Catherine
Background Wall, Art Abstract, Block Well & CC0 texture.
Source Ractapopulous
Prismatic Curved Diamond Pattern 8 No Background
Source GDJ
Remixed from a JPG that was uploaded to Pixabay by theasad121
Source Firkin
Tile-able Dark Brown Wood Background. Feel free to use it as a background image in your designs or somewhere on the web. By the way, the color seems to be close to Coffee Brown.
Source V. Hartikainen
From a drawing in 'La Principauté de Liège et les Pays-Bas au XVIe siècle', Société des Bibliophiles Liégeois ,1887.
Source Firkin
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
Background Wall, Art Abstract, Block Well & CC0 texture.
Source Ractapopulous
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
Nice little grid. Would work great as a base on top of some other patterns.
Source Arno Gregorian
Prismatic 3D Isometric Tessellation Pattern 6
Source GDJ
Heavy depth and shadows here, but might work well on some mobile apps.
Source Damian Rivas
Retro Circles Background 7 No Black
Source GDJ
The square tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
Derived from an image that was uploaded to Pixabay by Kaz
Source Firkin
Remixed from a drawing in 'Hungary. A guide book. By several authors', 1890.
Source Firkin
A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Derived from an image that was uploaded to Pixabay by Darkmoon1968
Source Firkin
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin