Keyword Search :
To search an electronic catalog or index by having the program search for terms (keywords) provided by the user. Keywords do not have to be standardized subject headings, and a keyword search often searches all data fields for the terms (eg, "winter" as a keyword might retrieve items with Winter in the author field as well as items with "winter" in the text or title). Keyword searching often allows flexible and powerful features such as Boolean operators, truncation, and field searching.
From : www.amberton.edu/VL_terms.htm