An anchor refers to a technique used to manipulate a user's ability to make an unbiased assumption. Anchors often are an unrealistic starting point (price or time) that cause users to regard other similar points as reasonable by comparison. Note that the term anchor is occasionally also used for hyperlinks, especially when refering to in-page links.
A typical example of an anchor is a overy high price on an item that is then placed on sale. The customer is tricked into assuming the item to be of higher quality because of the seemingly high price and considers the price as relatively low, knowing the item's price before putting it on sale. A customer might thus be made believe to a purchase is a bargain, while in fact, they pay a considerably high price.
Anchors are also commonly used in delivery estimates. The anchor is a high estimated time so that when packages arrive early, users are pleasantly surprised.