A subkeyword is a keyword or phrase subordinate to another keyword or phrase (the parent). A multi-level index consists of a series of these parent and subordinate keywords.
There are several ways to work with subkeywords including:
Index Designer: You can manually enter subkeywords directly into the Index Designer and link them to topics.
Topic Properties: You can add subkeywords to topics through their properties. For each topic, you open a dialog that includes an Index tab. From this tab, you can add both keywords and subkeywords.