Beautiful textile illusion by artist Timur Si-Qin!
This specific style of pattern is known as moiré. According to Wikipedia, moiré "is an interference pattern created when two grids are overlaid at an angle, or when they have slightly different mesh sizes." Simply, two sets of lines are superimposed over another set of lines. Illustrated example shown below, click through to view an animated demonstration.
Want to master Microsoft Excel and take your work-from-home job prospects to the next level? Jump-start your career with our Premium A-to-Z Microsoft Excel Training Bundle from the new Gadget Hacks Shop and get lifetime access to more than 40 hours of Basic to Advanced instruction on functions, formula, tools, and more.