relativo who, whom, which, what, that.
o filme do qual você gostou tanto / I saw the movie which you enjoyed so much.
interrogativo what, which: qual destes livros você quer? / which of these books do you want? qual é a altura daquele monte? / how high is that hill?
how, as, such as: tal qual você queria / such as you would have it.
nonsense, ridiculous: qual! bobagem / what!, fiddlesticks!