These are terms that only apply to advertising programs such as adwords - not seo. In adwords exact match means that your ad will be triggered only when someone types in exactly what you've specified, with no other words attached to it before or after, and if you've specified a phrase, with the words in the same order. A broad match means your ad will be triggered for synonyms of your keyword, and other related terms There is an inbetween option which is phrase match The only time you come across these terms in seo, is when you are using the Google adwords keyword tools. Broad match is the default setting, but it is meaningless for seo - you need to ALWAYS use exact match to get search volume estimates.
1. exact match - no other words in the search query - e.g. bp oil spill 2. phrase match - phrase with the words in that order in the search query - e.g. bp oil spill sucks, bp oil spill photos, effects of the bp oil spill
A broad search is like searching for "dog", you could get results for buying a dog, dog welfare, dog food etc. An exact search is something very specific like "Buy baker's dog food in London".
A broad match means that the words "one" two" "three" can appear anywhere on the page without regard of their proximity to each other. If all three words were not present on any webpage I suspect Google would deliver pages containing two of them. Exact match means that "one" two" "three" appear on the same page with a proximity of 1 word and in that exact order.