Hello,
What is keyword search?

A Keyword search looks for words anywhere in the record. Keyword searches are a good substitute for a subject search when you do not know the standard subject heading. Keyword may also be used as a substitute for a title or author search when you have incomplete title or author information. You may also use the Guided Keyword search option to combine search elements, group terms, or select indexes or fields to be searched.

Keyword research is the process of selecting the right keywords for your domain. Google keyword planner is the best free tool to select the correct keywords for your domain.