Hold on, that's "defend it or lose it". Author of libcurl clearly is using the name, there are new releases coming out quite often.
Re:Google to Reimplement Curl in Libcrurl
by nerdponx on Wednesday June 19, 2019 @11:07AM
(#20224019)
My wording was unclear, yes. If you aren't defending it, you aren't using it as a trademark.
Think of the term literally; if it's not exclusive to you, it's not longer a "mark" of your specific "trade". It's just a "mark".
But the law follows "use it or lose it" rules. If you don't defend your trademark, then in the eyes of the court it is no longer a trademark.