A Special Needs Trust (SNT) allows you to retain government benefits such as Medi-Cal and SSI, which you would otherwise not be eligible to receive because of government regulations. These trusts are created to ensure that you receive maximum benefits while still receiving other support.
There are two types of SNTs. The Third Party SNT is the most common, and is set up by someone other than the beneficiary. For example, a widow leaves her estate to her only son, who is currently on Medi-Cal. The widow will likely want to set up an SNT for her son to ensure he maintains benefits. Since the widow creates the trust for the son (the beneficiary), it is a Third Party SNT. A First Party SNT differs in that the money already belongs to the beneficiary. For example, if in the previous example, the son had an inheritance and put that money into a trust, then it would be a First Party SNT.
The most important part of any SNT is determining how to make distributions to the beneficiary without affecting government aid (or at least providing benefits that outweigh the cost of losing aid).