Basic Uniform Commercial Code
As defined by common law, a default is a failure to pay a debt as it comes due.
Default can be contractually defined however wished. (Requiring insurance, certain handling instructions, etc.)
After default, a secured creditor has a right to repossess and dispose of the collateral to satisfy the outstanding indebtedness.
If the loan terms or standard commercial dealings allow for a grace period, a failure to pay within the grace period does not constitute default.