Stop words are common words that are ignored by search engines in order to save storage space and to increase the speed of searches. Adverbs, conjunctions, prepositions or forms of word "be" are all stop words.
 
Examples: to, the, be, is, been, are, what, where, how, for etc.
 
Try to avoid using stop words in your searches because the filtering of the words by the search engines can impact your search results. Relevant listings could be filtered out. Also try to avoid using a category of words called contranyms. Contranyms are words that carry multiple meanings, one or more of which contradict each other.
 
Avoid using heteronyms, words that are spelled the same but have multiple pronunciations and meanings. An example of a heteronym is the word “lead”. When pronounced “leed”, it can mean several things such as a favorable gap (like in a race) or a prospective customer for your products (product lead).
 
When pronounced “led”, it obviously means lead, as in the metal.