A "stopword" is a term that a search engine will not include in a query because it's too common.
for eg. when you search for the onion, it will search for onion and omit "the" from its search.
You will get a message, "The" is a very common word and was not included in your search.
You can force Google to search for the by putting a + in front of it for eg. +the onion

" - " Searches
Sometimes what you're searching for has more than one meaning; "pet" can refer to plastic or animal. You can exclude a word from your search by putting a minus sign ("-") immediately in front of the term you want to avoid. (Be sure to include a space before the minus sign.)
For example, to find web pages about pet that do not contain the word "dog", type:
pet plastic -animal -dog

Phrase Searches
Search for complete phrases by enclosing them in quotation marks. Words enclosed in double quotes ("to be or not to be") will appear together in all results exactly as you have entered them.

"OR" Searches
Google supports the logical "OR" operator. To retrieve pages that include either word A or word B, use an uppercase OR between terms. For example, to search for a vacation in either London or Paris, just type:
vacation london OR paris