Windows 7's five years of extended support will expire on January 14, 2020: exactly one year from today. After this date, security fixes will no longer be freely available for the operating system that's still widely used.
As always, the end of free support does not mean the end of support entirely. Microsoft has long offered paid support options for its operating systems beyond their normal lifetime, and Windows 7 is no different. What is different is the way that paid support will be offered. For previous versions of Windows, companies had to enter into a support contract of some kind to continue to receive patches. For Windows 7, however, the extra patches will simply be an optional extra that can be added to an existing volume license subscription—no separate support contract needed—on a per-device basis.
These Extended Security Updates (ESU) will be available for three years after the 2020 cut-off, with prices escalating each year.