What short (two letters!) but powerful boolean operator can check whether or not one string can be found in another string?

OR

Explanation:

"OR" expands a search by telling the database that any of the words it connects are acceptable. This is particularly beneficial when you are searching for synonyms, such as "the victorian age" OR "sexual puritanism"

So, if you type in "the victorian age" OR "sexual puritanism", your results will include articles with either term, but not necessarily both.