This is the path a windows update follows to be released.
"Windows Client OS" refers to "current branch" on this schematic. They include every version of Windows 10 except the Entreprise and server versions to ensure that deploying them on companies that runs thousands of computers and servers wont have problems with them.
And even with this... They still have problems with them sometimes (i know we do where i work with Windows Entreprise at least :) But most of the time the problem comes with an incompatibility of an update with a proprietary software so not Microsoft's fault!).
Also there is a special version of Windows which is Windows 10 entreprise Long Term Service Branch (LTSB) that has reduced features (no windows store, no fancy options like "dark file explorer", no cortana...) to ensure maximum stability which most big companies which requires maximal security (like banks) are using.
Note that the time framed used in the picture above is for regular updates. For updates patching a 0-day vulnerability the time span is much lower.