The description of the "curious" badge is:

Asked a good question on 5 separate days, and maintains a positive question record.

First, what qualifies as a "good question"? Second, how does one maintain a positive question record? I am asking this because I just got the "curious" badge on the main site, but I have not asked any questions recently. Please enlighten me on this.

• See capital-m Meta. – user61527 Jul 2 '14 at 18:30
• I was notified today that I had earned a Curious badge. I should be immensely happy and grateful. However, I have never asked a question on the main site. Perhaps the program has another meaning of "He is curious" in mind. – André Nicolas Jul 2 '14 at 20:35
• @AndréNicolas You earned it on the meta site. Badges are separate for main and meta, unlike reputation. – user147263 Jul 2 '14 at 20:55
• The questions need not be recent. It does not matter how old they are. – user147263 Jul 4 '14 at 2:28

Per the announcement, positive question record means $$\frac{\text{total questions - negative questions - closed - deleted}}{\text{total questions}} \ge \frac12$$ That is, this formula triple-punishes for a question that has been downvoted, closed, and deleted.
A well-received question is one that's open, not deleted, and has a score $> 0$. If you ask at least one well-received question in a UTC day and none of your questions that day are deleted, downvoted, or closed, you get one more day of credit toward the badge.