What is an Estate Sale?

Wikipedia has a nice defination and explanation of what we do at an estate sale:

An estate sale or estate liquidation is a type of garage sale, yard sale or auction to dispose of a substantial portion of the materials owned by a person who is recently deceased, or who must dispose of their personal property to facilitate a move.
Reasons for an estate sale
The most common reason for an estate sale is the death of the property owner, and the consequent need to quickly liquidate that persons belongings. The survivors may have no interest in the bulk of the personal belongings left by the deceased, or may simply lack a place to keep those belongings. Where the survivors of the deceased cannot agree to the disposition of tangible property, a court may order those goods to be sold in an estate sale with the proceeds to be divided between the survivors. Such a sale and division may also be mandated in the will of the deceased.
An estate sale may also occur because the property owner will be moving into a situation where they will be unable to keep their property - for example, a move to an assisted living facility, a retirement community, a rest home or other living quarters.

Conduct
Estate sales are usually conducted by a professional, for a percentage of the revenues. The liquidator may also charge the estate back the costs to give said sale, including but not limited to advertising, marketing, research, labor, security, refreshments and other fees incurred in giving a successful sale. The presence of a professional liquidator may be necessary because the scope of the process is likely to be overwhelming to the survivors. Furthermore, the liquidator often has a tremendous loyal following of dealers, collectors and public. They may be familiar to buyers who have been coming to their sales for decades, and trust that they will price wisely and fairly and steer them toward finding their niches within each collectors realm, and for the specialist's knowledge and experience with pricing antique items, and general value knowledge of all types of household goods and personal property value, his or her following of customers, and the specialist's experience in disposing of unsold goods in an unsentimental manner after the run of the sale. These professionals often times take a percentage of the net proceeds anywhere from 20-50 percent due to their ability to double or even quadruple the gross sales outcome by their organizational presence.
Estate liquidators, when professional, honest, hard working and diligent can not only make the families or executors and heirs plenty of extra monies in giving a successful sale, at the same time a seasoned professional can often manage to keep all items out of too full landfills and dumps while managing to recycle and bring unwanted fairly worthless items into the hands of a second part of our poor community who wants and needs the dregs of most estates and can re home them rather than waste or bury them under dirt. Antique and collectible dealers use estate sales as one of their more important wholesale sources. Estate sales are typically 1 to 3 days long, often with a price reduction toward the end. It is becoming more and more of a trend on the west coast that on the last final day of the given estate sale, with the family's or executor's permission, all leftover items are advertised and given away for free to limit the amount of waste in any given purging situation. Sometimes this can result in an empty house and less burdened landfill. Moreover, estate sales are being used to redistribute households where families have lost their ability to pay mortgages and are losing their homes to foreclosures.