The broad match type is being used for PPC (pay per click) advertising through Google Adwords and other platforms. Adwords provides the option to target Exact keywords, Phrase, Broad (and Modified Broad). As a PPC account manager, you sometimes don't want to target just the Exact keyword, because targeting other variations of the KW (synanoms, plural, singular, mispelling, long tails etc) you did not think of, can generate more impressions for you, more clicks, and hopefuly more revenue. Of course, Broad match has it's downside: Google loves money, and many times your PPC ads are shown for Broad matches which are less relevant to your keywords... and can increase costs, while not always bringing the desired ROI.
So, when doing a KW research not for running Adwords campaigns, you shuld probably only look on the Exact match. Remmeber that Google Keyword Tool was built mostly for Adwords advertisers and this is why you can see the Broad match and Phrase match as well, although they are pretty much useless for you.