"To support the device" means to provide assistance, help or resources to make sure the device functions properly or achieves its intended purpose. Full definition
Sadly, if you were hoping for a change from the company's typical policy of supporting devices for up to 18 months, you're going to be disappointed. (digitaltrends.com)
As mentioned, the update is available for download now on supported devices. (9to5google.com)
We still don't know the name or an exact premiere date, but there is a public beta available for supported devices. (xda-developers.com)