The big update, that requires a long time to download, is/was the Fall Creators Update. Microsoft released it in mid-October but, because their servers couldn't possibly cope if every Windows computer in the world was downloading it simultaneously, it's been offered to different people at different times (using what's called a 'roll-out release' So it's possible that you could be one of the last to get it (but see below as well).
That update was meant to enhance Windows 10 with better privacy features
http://www.techradar.com/news/windows-10-will-get-a-privacy-boost-with-fall-creators-update
more tools for those who, through disabilities, struggle to use computers
http://www.techradar.com/news/fall-creators-update-aims-to-make-windows-10-more-accessible
and a new look (called 'Fluent Design')
http://www.techradar.com/news/heres-what-windows-10-will-look-like-with-the-fall-creators-update
However, like everything from Microsoft, even the fixes need fixing, so there's now an update to the Fall Creators Update (so, if you've already got the big update, it could just be the fix for it that you're being offered):
https://www.windowscentral.com/microsoft-rolls-out-fall-creators-update-fixes-new-cumulative-update
One of the problems with Windows updates is that (because Microsoft integrates things like Internet Explorer ,Edge and Outlook into Windows itself) you end up downloading fixes for programs that you never use anyway. (e.g. if you only use Firefox or Chrome, you don't need an update for Internet Explorer).
If you want to stop Windows from downloading all but the really essential updates, you should tell Windows that there's a data cap on your internet usage (even if there isn't). Scroll down to 'How to Set a Wi-Fi Connection as Metered' and 'How to Set an Ethernet Connection as Metered' here:
https://www.howtogeek.com/226722/how-when-and-why-to-set-a-connection-as-metered-on-windows-10/
While you're doing that, those of us who decided to steer well clear of Windows 10, and stick with Windows 7, will all sit back with big grins on our faces ;-)