In general: the stronger the colour, the more serious or higher impact.

The labels are grouped as follows.

• bug -- something that should work but doesn't
• enhancement -- something that could be added to make it better (aka a feature request)
• question -- a query about how something works
• refactor -- a rearrangement or rewriting of the code that doesn't have a direct effect on its use

Then, independently,

• dogfood -- this issue arose from weavework's own use of flux
• help wanted -- this is fairly self-contained and probably doesn't need a lot of background or context to fix

• high user impact -- directly affects users, in the bad way
• nice to have -- not urgent or especially important, just pleasant

• vague -- not described well enough to address, at present
• duplicate -- there's already an issue addressing this (this issue should be closed)
• invalid -- this issue doesn't apply or doesn't make sense (this issue should be closed)
• wontfix -- an executive decision was made not to address this (this issue should be closed)
• blocked(-decision) -- this cannot move forward until some out-of-band decision or action is taken
• yolo -- why the heck not? wheeeee
• boot for now -- feel free to punt this down the road (deal with it indefinitely later)

• size/small -- probably less than a day's work, either mechanical, localised, or both
• size/medium -- a week or so's work; might need changes to APIs or protocols, or rewrites of packages
• size/large -- changes to architecture, large-scale rewrites. Weeks or months of work.