A creationist, in the broad sense of the term, is anyone who affirms that God created anything. The most ardent Christian Darwinist is a creationist but the word isn’t regularly used in the broad sense. Creationism is popularly referred to as young earth creationism, that is, that the universe is 6-10 thousand years old.
I’m an old earth creationist (big bang theism [ID]) in the midst of thousands of young earth creationists. I believe that the big bang (standard model, 13.7 GYA) is the correct model that describes the beginning of the universe. I’m a proponent of intelligent design though I’d consider myself a soft-agnostic with respects to early anthropology. I’m open to common descent but my biggest hurdle to that is the Cambrian explosion.
Though I disagree with young earth creationism on many different levels I find it to be a peripheral issue in Christianity. It doesn’t interfere with the existence of God, the gospel, or sanctification in any way. I do get a little frustrated when creationists attempt to make it a gospel issue (though I’ve never met one personally, I’ve read it in the popular creationist literature). The implications in holding to a young earth position are vast and depending on what one’s reasons for holding to it may affect one’s epistemology and modus operandi in science (unwarranted a priori commitments, the Bible isn’t a science book) to name a few. In the end I find it to be an untenable position but most of my friends are creationists and we get along fine, we just simply disagree. I hope that young earth creationists, big bang theists (ID), and theistic evolutionists can function peacefully and not allow this to be as big of a dividing issue as it is today.
It’s always fun to see someone’s reaction when they find out I believe the big bang actually happened and that I’m open to the reality of the multiverse. If I’m the leak to the world than so be it, but there’s quite an underground network of big bang theists here at my university, we just learn to keep it hush-hush at certain times (so don’t generalize!).