A Meta-term is a term that cannot be used in the indexing process. It is a term to describe other terms, for example guide terms, facets, categories, etc.
When adding a new term it can be made a Meta-term by ticking the checkbox besides “Meta-term”.
When going to Menu -> Administration -> Vocabulary configuration and clicking on the name of the vocabulary the option “CFG_SEARCH_METATERM” can be found. To make Meta-terms searchable select “YES” from the drop-down menu.