The Boolean Search Facility allows queries to be formed from arbitrary Boolean expressions containing the keywords "+" ,  "," ,  "-"
Example : -

excise,customs

finds records containing 'excise' or 'customs'

excise+customs

finds records containing both 'excise' and 'customs

customs+exim-excise

finds records containing 'customs' and 'exim' but not 'excise'

excise customs
        finds results containing excise custom as phrase.