A Neologism can be a few different things. It can be a new word, a new way someone uses a word, or a new type of phrase.
It is derived from the Greek word, Neo, which means "New."
A Neologism in the sense of a new word would be, for instance, Chumbling. This is chewing and mumbling at the same time. In this, it is also a compound word, however, it is a new or recent word. In the sense of a new use of a word, look at the use of the words in the Urban Dictionary. These are all neologisms. This also applies to the phrases. The Urban Dictionary, in it self is a Neologistic source.