A no-fault divorce is one in which no party involved is at fault. Long ago, it was common for someone to be responsible for the reason the marriage failed. This could include things like infidelity, cruelty, or abandonment. In those times, the court would agree that one party was at fault, dissolve the marriage, and award the non-guilty party with benefits from the settlement.
Today, people can follow a no-fault process to dissolve the divorce when things like irreconcilable differences occur. In this case, neither party is considered responsible.