By default the search on confluence assumes 'OR' between multiple words in the query. Most search sites (like Google) realized in about 1998 that most people want (and now expect) the default to be 'AND'. The default should be 'AND' and of course it would be best if this were configurable per instance or per space.

Also, it seems that some 'word stemming' is done by default. It would be nice to be able to turn that off. An example which we have seen here is someone searching for the name 'Walles' which matched a page with 'Wall' in the title, strange and unexpected!!