Alternative grammatical forms of words are extracted and added to the document in a separate document section to enable searching for other grammatical forms than that given in the query string.
Lemmatization is the aggregation of different word forms to enable search across different forms of the same word (such as products and product). Lemmatization enables searches to match documents with similar meaning, but different word forms in the document or the query. Lemmatization has similar effects as stemming, but is more precise, as it based on dictionaries. Generally speaking, lemmatization means the mapping of a word to its base form and / or all its other inflectional forms.
The purpose of lemmatization is to enable that a query for one of the possible forms of a word will also match documents that contain a different form of the word. This allows a user to search for a term like car and get both documents that contain the word car and documents that contain the word cars.