EndNote Online is a web-based counterpart to EndNote, the desktop application. When you save references to EndNote Online, you are saving them to servers located "in the Internet cloud" (i.e., NOT locally at the UMCG). This means you can get to your EndNote Online library from anywhere you have Internet access. 

When to use EndNote Online?
We recommend creating an account at EndNote online. This is because you can then synchronize your library online (and thus have it as a back-up). Also if you want to share your library or just a group you need an EndNote online account to do so. When you want to use EndNote in Google Docs or when you want to share your library you will need to set up your EndNote online account.

Users may set up a free EndNote Online account by registering at: https://web.endnote.com/

Sync option
Once you have set up an EndNote Online account, you may integrate this account with your EndNote desktop application using the "Sync" function to facilitate the transfer of resources between EndNote Online and EndNote.

When using EndNote 21 (or later) and synchronising your library you get access to the new online environment of EndNote. You can find it here: http://web.endnote.com/.