Trusts can be short term but most are designed to last for many years or for generations. Trusts are often created during the life of the Grantor by writing a Trust Agreement which names a Trustee to be responsible for carrying out the Trust terms, and transferring assets to fund the Trust.
Estates are created only after the death of an individual. During life the individual may write a Will naming an Executor who like a Trustee has the fiduciary responsibility to see that all the terms of the Will are carried out including: collecting all the deceased's assets, paying all outstanding bills, dividing personal property (e.g. jewelry), paying any final income taxes, paying estate taxes, and distributing all the assets as the deceased instructed in the Will. An Estate, unlike a Trust, is typically short term, lasting two to four years. Unlike a Trustee, the Executor rarely makes long term investment decisions as their job is to preserve the assets until they can be distributed. [Note: if an individual dies without having written a Will, each state has laws directing how their assets are to be distributed. Typically a probate court will appoint a Public Administrator to see that the assets are distributed by law after all expenses are paid.]
Sometimes Trusts can act like Estates. In many states (like Florida and California) it is customary to create a Revocable Trust during life and transfer most of the individual's assets into the Trust. A Will is usually also drafted, but it has a limited purpose of gathering any assets not already in the Trust and transferring ("pouring") them into the Trust. The Trust then does all the work of the typical Estate (and the Trustee all the work typically done by an Executor). Here the Trustee ends up with all the deceased's assets and so is responsible for paying any outstanding debts of the deceased including income taxes, paying any estate taxes, and distributing the balance of the Trust. Often this type of Trust will be written to fund and operate continuing Trusts for descendants or charities.
And sometimes Estates can act like Trusts when the Will directs the Executor to take the remainder of the deceased assets, after all expenses, and fund continuing Trusts. A Trustee (who may or may not be the same person as the Executor) is named to manage these Trusts, and the Will, because it contains all the instructions necessary to administer the Trusts, becomes the Trust Agreement.
Every Estate Plan Deserves 'Great Administration.