What it means
That lovely little fake resurrection when you were fully cooked, ready to tap out, and then your body suddenly coughs up a bonus round of energy. You hear it in running, gym chat, long shifts, and nights out when someone goes from zombie mode to weirdly alive again. It doesn't mean you're fresh, just that you've found another gear for a bit.
Usage examples
"Thought I was done by mile six, mate, then a second wind hit and I flew home. Felt proper heroic till I got in and melted."
"I was shattered by nine, then got my second wind and danced till two."
"Halfway up the hill she found her second wind and powered to the top."
"I was dead on my feet after that shift, then got a second wind and ended up reorganising the whole kitchen at midnight."
"We nearly bailed after the pregame, but Jess caught a second wind and suddenly had us hunting for one more pub."
Where it comes from
It comes from running and exercise talk. In the late 19th century, people were already using second wind for that point where the first wave of strain eases off and you can keep going with renewed energy. From there it spread into everyday English for any surprise comeback burst when you thought you were spent.
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