What is a cash loan from a life insurance policy?

A "cash loan", as you have called it, is a loan based upon the cash value of a whole life insurance policy. Only whole life insurance policies (not term policies) accumulate cash value. Each premium payment is allocated between the cost of providing the indemnity protection (the "pure" protection), the administrative costs of the company, and what may be considered a "savings" element that is built into the policy. But do not confuse the "savings" element with a real savings account, because it is not; insurance is protection, not an investment. The cash value builds slowly at first but more rapidly as the policy matures.

All of that said, whole life policies generally allow for policy loans against the cash value of the policy. The loans bear interest at a rate stated in the policy. They need not be repaid, but if they are not, the accumulting interest eats away at the indemnity benefit. Likewise, if the loan is not repaid at all, upon the insured's death, the principal amount of the loan plus accrued interest is deducted from the indemnity benefit paid to the beneficiary(ies).