Not a flat you live inside, like in the UK – but a flat piece of cardboard.
Source Appleshadow
Zero CC tileable yellow craft paper; scanned and made by me. CC0
Source Sojan Janso
Light square grid pattern, great for a “DIY projects” sort of website, maybe?
Source Rafael Almeida
Prismatic Geometric Pattern Variation 2 With Background
Source GDJ
A pattern derived from repeating unit cells each derived from part of a mosaic in paint.net. The starting point for the mosaic was a picture of some prawns!
Source Firkin
I love these crisp, tiny, super subtle patterns.
Source Badhon Ebrahim
Embossed lines and squares with subtle highlights.
Source Alex Parker
With a name like this, it has to be hot. Diagonal lines in light shades.
Source Isaac
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
The act or state of corrugating or of being corrugated, a wrinkle; fold; furrow; ridge.
Source Anna Litvinuk
Small dots with minor circles spread across to form a nice mosaic.
Source John Burks
The following repeating website background is colored in a blue gray color and resembles a concrete wall or something similar to it.
Source V. Hartikainen
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
Remixed from a drawing in 'A Child of the Age', Francis Adams, 1894.
Source Firkin
Prismatic Polka Dots Mark II 2 No Background
Source GDJ
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Beautiful dark noise pattern with some dust and grunge.
Source Vincent Klaiber