Docked means that your phone is connected to a dock, a type of phone accessory.

What is dock mode in Android?

Dock Mode is a feature that can be found on some phones including many of the Samsung phones. Dock Mode is different on different phones but it often turns your phone into a desk clock, photo slideshow viewer, or music player. You can also set it as a speakerphone when you receive calls.

What is docked in Mobile?

When a device is docked, the kernel driver fires an event or modifies the file state, which make the Android system notice it, then it will broadcast the event to the apps system-wide.