Variable universal life insurance (often shortened to VUL) is a type of life insurance that builds a cash value. In a VUL, the cash value can be invested in a wide variety of separate accounts, similar to mutual funds, and the choice of which of the available separate accounts to use is entirely up to the contract owner. The 'variable' component in the name refers to this ability to invest in separate accounts whose values vary—they vary because they are invested in stock and/or bond markets. The 'universal' component in the name refers to the flexibility the owner has in making premium payments. The premiums can vary from nothing in a given month up to maximums defined by the Internal Revenue Code for life insurance. This flexibility is in contrast to whole life insurance that has fixed premium payments that typically cannot be missed without lapsing the policy (although one may exercise an Automatic Premium Loan feature, or surrender dividends to pay a Whole Life premium).
Variable universal life is a type of permanent life insurance, because the death benefit will be paid if the insured dies any time as long as there is sufficient cash value to pay the costs of insurance in the policy. With most if not all VULs, unlike whole life, there is no endowment age (the age at which the cash value equals the death benefit amount, which for whole life is typically 100). This is yet another key advantage of VUL over Whole Life. With a typical whole life policy, the death benefit is limited to the face amount specified in the policy, and at endowment age, the face amount is all that is paid out. Thus with either death or endowment, the insurance company keeps any cash value built up over the years. However, some participating whole life policies offer riders which specify that any dividends paid on the policy be used to purchase "paid up additions" to the policy which increase both the cash value and the death benefit over time.
If investments made in the separate accounts out-perform the general account of the insurance company, a higher rate-of-return can occur than the fixed rates-of-return typical for whole life. The combination over the years of no endowment age, continually increasing death benefit, and if a high rate-of-return is earned in the separate accounts of a VUL policy; this could result in higher value to the owner or beneficiary than that of a whole life policy with the same amounts of money paid in as premiums.