Sentence:  If we reverse the positions of <code>$a</code> and <code>$b</code>, the <WSD>spaceship</WSD> will sort in the opposite order... 
Meaning of the word marked with <WSD> tags:  The operator <code><=></code> in the Perl, PHP and Ruby programming languages, which compares two values and indicates whether the first is lesser than, greater than, or equal to the second.