Regex: what does (?! …) mean?

Question

The following regex finds text between substrings FTW and ODP.

/FTW(((?!FTW|ODP).)+)ODP+/

What does the (?!...) do?

Answer 1

The programmer must have been typing too fast. Some characters in the pattern got flipped. Corrected:

/WTF(((?!WTF|ODP).)+)ODP+/