The answer to what is a trust fund, is a rather easy one to answer, the short answer is that it is a fund that is set up to pay for a certain set of expenses such as college after such time as your death. Often parents will set one of these up in case something happens to them before their child grows up. The person that is in charge of the trust fund will be responsible for the paying of bills for the child until such time as they reach the age that they can take control of the fund. This age is around 18 for many of these trust funds.
This is designed to help deflect a few of the costs that are associated with the death of parents or other loved ones. There can be a number of these set up for more than just a child. There can be funds set up for an organization or a charity that the person in question has set aside as being close to them in a number of ways. The attorney in charge of managing this can dole the money out as they see fit or can dole it out according to a set of instructions that have been set up for the person in question. These are known as a letter of instruction. The attorney will generally be the one that has this letter.
A trust fund will be a great way in assisting a person to get the most from their death and make sure that the people or places that they have set aside money for will be the ones that actually get the money. These instructions will need to be explicit and will need to be part of the will at the time of the person's death. Now that you know about this, you will not be confused in the dealing of this in the long run.