what is broad keyword?

Broad match is the default match type that all your keywords are assigned if you don't specify another match type (exact match, phrase match, or negative match). Google AdWords system automatically runs your ads on relevant variations of your keywords, including synonyms, singular and plural forms, possible misspellings, stemmings, related searches, and other relevant variations.

Broad Keyword the matching option the more traffic potential that keyword.that allows your ad to show when someone searches for that keyword.