A trust is an arrangement under which one person, called a trustee, holds legal title to property for another person, called a beneficiary. You can be the trustee of your own living trust, keeping full control over all property held in trust. To learn more about serving as a trustee, see Nolo's The Trustee's Legal Companion.
A "living trust" (also called an "inter vivos" trust) is simply a trust you create while you're alive, rather than one that is created at your death.
Different kinds of living trusts can help you avoid probate, reduce estate taxes, or set up long-term property management. For details on creating a living trust, see Nolo's article Making a Living Trust: Can You Do It Yourself?