The articles about Fourier series and Fourier transform currently begin with:

> A Fourier series is a series expansion of a periodic function into a sum of trigonometric functions. The Fourier series is an example of a trigonometric series. By expressing a function as a sum of sines and cosines, many problems involving the function become easier to analyze because trigonometric functions are well understood.

and

> In mathematics, the Fourier transform (FT) is an integral transform that takes a function as input, and outputs another function that describes the extent to which various frequencies are present in the original function. The output of the transform is a complex valued function of frequency. The term Fourier transform refers to both the mathematical operation and to this complex-valued function. When a distinction needs to be made, the output of the operation is sometimes called the frequency domain representation of the original function. The Fourier transform is analogous to decomposing the sound of a musical chord into the intensities of its constituent pitches.

The introductory paragraph in Simple English is: 'A diamond (from the ancient Greek αδάμας – adámas "unbreakable") is a re-arrangement of carbon atoms (those are called allotropes).' Seriously?

Compare with the Britannica one: 'diamond, a mineral composed of pure carbon. It is the hardest naturally occurring substance known; it is also the most popular gemstone. Because of their extreme hardness, diamonds have a number of important industrial applications.'

Britannica concisely summarizes the basic knowledge about diamonds in an easy-to-read short paragraph.

I in fact sometimes do switch to simple english

The wikipedia is more information dense, but that's not always what I want in a general purpose reference. Also hyperlinks are good if you want to read the article. But I don't want to have to click through hyperlinks, and thereby lose focus. Sometimes I just want to know just enough to complete the context in which some thing was mentioned. In the opening sentence there's a whole phrase "solid form of the element carbon" hyperlinked - to what is not immediately clear - but curiosity peaks the mind and I see that it's to an article on carbon allotropes. Later on it says it's "metastable" so I need to know what that means, but it just links to an article that's equally obstruse and so I have to go on an endless rabbit hole of hyperlinks. Britannica usually explains briefly in parentheses what some piece of jargon means.

Let me point out, that for me personally, for many years, hyperlinks in Wikipedia were the worst feature. I hated that! Anytime I started looking for something, I would start following links ad infinitum. Was extremely distracting. Instead of a little inline definition, for everything is a link. There is a good balance between linking to the definition of each word, and just inlining the definition.

Anyway, at some I disciplined myself to not follow the links. But sometimes the definition really needs following them.