When you use broad match, your ads automatically run on relevant variations of your keywords, even if these terms aren't in your keyword lists. This helps you attract more visitors to your website, spend less time building keyword lists, and focus your spending on keywords that work.
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). The Google AdWords system automatically runs your ads on relevant variations of your keywords, including synonyms, singular and plural forms, possible misspellings, stemmings (such as floor and flooring), related searches, and other relevant variations.