When you optimize a page with keywords and phrases for SEO, you can use a combination of single words, plurals, synonyms/related keywords, mis-spellings, etc.

However, some words are impossible to optimize, they simply do not exist.  Take a look:

impossible to seo in the english language

More oddities here.

About 

INTERESTED in working with me on your Facebook Ads Business Acceleration? Sign up for a FREE breakthrough session! Learn More About Our Online Sessions.
===
Entrepreneur Magazine says Jon Rognerud is one of the most sought-after Digital Marketing Experts. His clients extend from high-end brands and middle-tier businesses in both B2B and B2C. His SEO website optimization book, "The Ultimate Guide to Optimizing Your Website" from Entrepreneur Press is in bookstores now.