Variable universal life is permanent life insurance built on the universal life chassis, with the policy value invested in separate-account subaccounts chosen by the owner rather than credited at a rate the insurer declares. NAIC's Glossary of Insurance Terms defines it as a product that "combines the flexible premium features of universal life with the component of variable life in which excess credited to the cash value of the account depends on investment results of separate accounts," and adds that "the policyholder selects the accounts into which the premium payments are to be made." Everything universal life does with a running account, this product does with a running account whose balance moves with securities markets.
The naming is worth pinning down, because the market and the regulators use different words and a reader searching one will not find the other. Consumers, agents and insurers say variable universal life, or VUL. The Securities and Exchange Commission regulates the class under a broader label: 17 CFR 230.498A(a) defines a "Variable Life Insurance Contract" as "a life insurance contract, issued by an Insurance Company, that provides for death benefits and cash values that may vary with the investment performance of any separate account." That definition reaches scheduled-premium variable life as well, so it is wider than the market term. NAIC's glossary keeps both, carrying "Variable Life Insurance" and "Variable Universal Life" as separate entries.