A neologism is a made-up or new word. Neologisms can be fun-ti-ful, but the problem is making sure others understand what you mean.
The word neologism was once a neologism itself. It was created by gluing the French prefix neo- onto the Greek logos or "word." People coin neologisms all the time, linguists track which ones stick, and eventually, we all feel they're old friends. Or maybe not: random samples from words coined in 2003 include: adultolescence, pastability, pre-zactly, and neomaxizoomdweebie.