When you are manually tagging campaigns with tracking variables, the value of the utm_term returns the value of the assigned keyword. If you are using AdWords with auto tagging enabled or if the user comes via a search engine the keywords used by the user to reach your site are displayed as the value, otherwise the value is set to (not-set). This dimension can also be used in the Google Analytics segments feature.

When written in queries it appears as:

ga:keyword