Not a flat you live inside, like in the UK – but a flat piece of cardboard.
Source Appleshadow
Light gray version of the Binding pattern that looks a bit like fabric.
Source Newbury
Prismatic Geometric Pattern Background 2 No Black
Source GDJ
From a drawing in 'Artists and Arabs', Henry Blackburn, 1868
Source Firkin
Based on an image that was uploaded to Pixabay by devanath
Source Firkin
Remixed from a drawing in 'Paul's Sister', Frances Peard, 1889.
Source Firkin
Just the symbols of the signs of the zodiac distributed in a chequer board-like pattern
Source Firkin
Looks a bit like concrete with subtle specks spread around the pattern.
Source Mladjan Antic
Prismatic Abstract Geometric Background 4 No Black
Source GDJ
Derived from an image that was uploaded to Pixabay by Kaz
Source Firkin
Continuing the geometric trend, here is one more.
Source Mike Warner
A seamless pattern formed from a square tile. The tile can be retrieved by selecting the rectangle in Inkscape and using shift-alt-I.
Source Firkin
From a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
Very dark pattern with some noise and 45-degree lines.
Source Stefan Aleksić
Prismatic Basic Pattern 2 No Background
Source GDJ
Vector version of a png that was uploaded to Pixabay by pencilparker
Source Firkin
Formed from decorative divider 184 in paint.net. Vectorised with Vector Magic.
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
An emulated “transparent” background pattern, like that of all kinds of computer graphics software.
Source AdamStanislav
A seamless pattern from a tile drawn in Paint.net and vectorised in Vector Magic
Source Firkin
A seamless pattern recreated from an image on Pixabay. It is reminiscent of parquet flooring and is formed from a square tile, which can be recovered in Inkscape by selecting the ungrouped rectangle and using shift-alt-I together.
Source Firkin
A repeating gloomy background image. This one consists of a pattern of black chains layered on top of a dark textured background.
Source V. Hartikainen