cloudflare and clos networks

After de downtime of 19 datacenters of cloudflare today it came appareant that cloudflare uses a (widely used) clos network. Now if you google the term you will find as a first hit the wikipedia which describes a clos network. It's correct but not the most easy page to read neither.

Therefor it's always nice if somebody else can explain it way simpler than wikipedia so enjoy this read here.