The phrase "unknown quantity" means someone or something that is not well-known or understood, making it difficult to predict or measure. Full definition
No one wants to deal with unknown quantities, those who may be seeking exposure for short - term gain. (blog.publishedandprofitable.com)
He refers to the need to provide future protections for children who are playing these types of games and spending extra money on unknown quantities. (cinemablend.com)
A code cracking style algebra worksheet using shapes rather than letters to represent unknown quantities. (tes.com)