Word co-occurrence measures the number of times groups of words (usually pairs) occur together in documents.
A collocation is the name given to a pair, group, or sequence of words that occur together more often than would be expected by chance. A collocation is the name given to a pair, group, or sequence of words that occur together more often than would be expected by chance.
The term association measures that are used to find collocations are discussed in chapter 6