Commingling is a term used for when a person's separate property, such as a personal inheritance, is placed in the same account or used to buy something as the community property such as earnings from the marriage or domestic partnership.
For example, a common occurrence is when one person uses money from the sale of house prior to the marriage or domestic partnership to put a down payment on a new house after the marriage or domestic partnership. In this situation the down payment is considered to still be separate property. However, is the mortgage payments for the new house have been made from the earnings that you and your spouse/domestic partner have accumulated during your union, then the value of the house is that was gained from paying down the house with that joined asset is considered to be community property but the combined equity of the house is thought of as commingled.
Situations like these can be very complex and it's best go the advice of a lawyer as they can better assist you with the details of the division of your property.
For more information on commingling and property division contact the property division lawyers in Orange County.