Dissolution refers to when an entity reaches its legal termination.
There are a wide range of agreements or situations that can reach dissolution. For example, contracts can reach dissolution, marriages can reach dissolution, corporations can reach dissolution, etc.
Once dissolution is reached, for all legal intents and purposes, the particular thing no longer exists.
Typically, dissolution occurs when something has gone wrong. For example, if dissolution is occurring in regard to a corporation, it is usually because the corporation has failed and has gone bankrupt. If dissolution of a marriage occurs, it's typically because the marriage has failed and the two people no longer wish to be married to one another.
Once dissolution is reached, certain legal protections and rights that existed before the dissolution may no longer apply.