What does surge mean?

when you draw a card with 'surge' on you draw another card from the encounter deck

rich

Here's the definition from p. 24 of the rules:

"When an encounter card with the surge keyword is revealed during the staging step of the quest phase, reveal 1 additional card from the encounter deck. Resolve the surge keyword immediately after resolving any when revealed effects on the card."

So, as rich explained, surge forces you to reveal and resolve another encounter card.

However, be aware that Thalin ability resolves before the surge keyword.

So if the card revealed with Surge is an enemy with only 1 hit point, then the surge keyword doesn't has it effect