So here is my short explanation.
Windows 10 has two update types:
- Feature updates (also known as ugprades), these add new features to Windows 10 operating system and upgrade the OS build;
- Servicing updates. These are regular security and reliability updates and they are similar to what we have seen in previous Windows OSes.
Windows 10 has three different configuration options, they differ how feature and servicing updates are received:
- Current Branch (CB). This option receives feature updates immediately. Servicing updates (this includes security updates) for this option are available for approximately four months. So you must upgrade to next CB build to stay supported and receive servicing updates.
- Current Branch for Business (CBB). Feature updates are received approximately four months later than CB. Servicing updates are available for at least eight months.
- Long Time Servicing Branch (CBB). Does not receive feature updates. Servicing updates are available for at least ten years. This options is only available if you use Windows 10 Enterprise.
Here is a bit more thorough explanation by Microsoft: https://technet.microsoft.com/en-us/itpro/windows/manage/introduction-to-windows-10-servicing