What is haiku?

After entering my haiku for a contest held by the @Romance profile, I realized I had a little talent... Writing haiku(s)!!! Please note that my inspiration juices come once in a while, but I'll try to let it flow often. :-)

Edit November 2016:
Even though I just started writing this last year, it already feels so cringy.
So, I'm not gonna write more haikus in this book to preserve its childishness.