These new BestMatch vocabulary files actually have over 45,000 words instead of the standard 30,000 words. In the Professional Edition of Dragon NaturallySpeaking version 3.0, you also have the choice of using an even larger vocabulary file which has over 64,000 words. The 64,000 word vocabulary also has even more statistical information relative to the number of words than 45,000 word vocabulary included in the Standard Edition and the Preferred Edition. However, the larger vocabulary files also require additional memory. And I would allow for 16 MB of additional RAM when using the 64,000 word vocabulary in the Professional Edition.
Trigrams are the name of statistical data that models the probability of words in sets of three.
The addition of trigrams makes Dragon NaturallySpeaking that much more accurate in the presence of homonyms. This means that Dragon NaturallySpeaking version 3.0 is much less likely to mistake a command for dictation or vice versa. This is optional, but if you have a very fast processor, you can change the tradeoff between speed and accuracy to take advantage of your additional resources. In summary, BestMatch is the name of the improvements in Dragon NaturallySpeaking version 3.0 which improve your accuracy. Dragon Systems internal tests indicate that when using the larger acoustic models and larger vocabularies along with the other improvements in version 3.0, users experience approximately 25 percent fewer errors.