Let's see if I can do this objectively - I am one...
A creationist is one who believes that the Universe, the earth, life and all that sort of stuff were created by a higher being (for example, God). The alternative non-creationist hypotheses are: it is has always been around (steady state theory); it just formed spontaneously (e.g. big bang); or it is all a figment of our own imagination (philosophy).
There are several flavours of creationist: not all are strongly attached to the much-ridiculed calculation of Bishop Usher's that the world was created one afternoon in 4004BC. These are called young earth creationists. These tend to form the majority of seven-day creationists who believe that the earth (and usually the universe) was created in six days plus one day rest as in Genesis 1.