The term "Lightning" is a broad brand comprising many different technologies.
How do we approach this as a community especially when it includes:
UI - Lightning Component Framework - Lightning App Builder - Lightning Extensions (coming)
Backend Services - Lightning Connect
Tools - Lightning Process Builder - Lightning Schema Builder - Lightning Communities Builder
For the first time, I saw this tag appear today, which, if you ask me, is not useful for categorizing anything.
https://salesforce.stackexchange.com/questions/tagged/lightning