"Uninvested cash" refers to money that is not currently being used for investment purposes. It is cash that is held in a bank account or kept on hand without being actively used for buying stocks, bonds, or other investments. Full definition
It is typically not the only option available for uninvested cash, and the Securities and Exchange Commission (SEC) has issued an Investor Bulletin to inform investors about the characteristics and risk of these programs. (aaii.com)
Uninvested cash in your account is held in what is known as a core position. (fidelity.com)
Fidelity Government (available for use as a core position in a retirement or non ‐ retirement account, used for processing cash transactions and for holding uninvested cash) (fidelity.com)