How is it that I can enter a word and a search results page appears that is helpful but does not include the search term as such?

When you enter a search term, our intelligent search facility compares it both with the designations for the existing categories and with the terms that are linked to these. A category is linked to as many as 25 search words. These include, for example, synonyms, abbreviations and words with a similar meaning. You may therefore see a search results page, even though the search term itself does not appear on it.
Example: you enter “chopper” and categories that include “helicopter” are displayed.