The expression ‘OR’ allows you to search for more than one piece of information at the same time.
Suppose that you wanted to either go cycling or play tennis in Manchester.
To go cycling in Manchester you might use this search term:
cycling manchester
To play tennis in Manchester, you might use this search term:
tennis manchester
To find either cycling or tennis in Manchester you could use this search term:
cycling tennis manchester
However, this might not work, because the search term you have specified is actually:
cycling AND tennis AND manchester
The search engine would look for webpages that contain all three keywords, ie places in Manchester where you can both cycle AND play tennis. Such a place might not exist.
A better way is to combine the two searches by using the Boolean expression ‘OR’:
cycling OR tennis AND manchester
This search term would give you results showing you where you could cycle OR play tennis in Manchester, giving you a better chance of finding what you are looking for.