A "Trust" refers to the legal entity which arises when an individual or entity (known as the "Trustee") is designated with the responsibility of managing assets and/or income for the economic benefit of another (known as the "Beneficiary") in accordance with a written trust instrument. Essentially what happens is the Trustee holds legal title to the property while the Beneficiary holds equitable title. The Trustee generally has a fiduciary duty to deal with the property for the benefit of the Beneficiary.
A Trust can be used when one wishes to ensure the needs of a loved one are met when that loved one is unable to manage property on his own. It is also a mechanism that can be used to avoid taxation in estate planning.
A Trust created in your will is called a "Testamentary Trust" and the trust provisions are contained in your will. Many parents and grandparents create a trust in their will for the benefit of their children/grandchildren to ensure that the funds are used to support and educate the children according to their respective needs before the eventual distribution when the children reach an age of sufficient maturity to handle assets.
The term "Revocable Living Trust" refers to a trust which you create during your lifetime, and which you can revoke or amend whenever you wish to do so. You can also create an "Irrevocable Living Trust" which is permanent and unchangeable. Either type of Trust may be designed to accomplish the purposes of property management, assistance to the Grantor (one who creates the Trust) in the event of diminished physical or mental capacity, and distribution of the property after the death of the Grantor.
The choice of what type of Trust to create should be made after careful consideration of the various factors relating to your goals and circumstances. Take the time to discuss this with your attorney before making any decision.