The term "killer" is sometimes used as a more vivid synonym.
A cancellation intended solely to prevent reuse of a stamp is sometimes called an obliteration.
Many early cancellations were pen cancels, simply the use of a writing pen to deface the stamp, but before the days of ball-point pens, these took longer to apply than a handstamp, and most postal administrations required the use of cancellation devices, either supplied by the administration, handmade by the postmaster, or purchased from specialized suppliers. Handmade cancels were typically carved from cork and are known in a bewildering variety of creative designs, collectively known as fancy cancels. Pen cancels may still occasionally be seen (sometimes done with marker), typically when a postal clerk notices that a stamp has not been touched by the automated machinery (though there have sometimes been complaints by stamp collectors of redundant pen cancels by overzealous postal employees).
In the early period of the issuance of postage stamps in the United States a number of patents were issued for cancelling devices or machines that increased (or were purported to increase) the difficulty of washing off and reusing postage stamps. These methods generally involved the scraping or cutting-away of part of the stamp, or perhaps punching a hole through its middle. (These forms of cancellation must be distinguished from perfins, a series of small holes punched in stamps, typically by private companies as an anti-theft device.) See postage stamp reuse.
United States patent number 6672623, "Modification of receiver surface to reject stamp cancellation information," is "a method and apparatus for [placing a] protective coating is over the... image area [of personalised postage with the personalised image] such that official cancellation mark placed over the second area will not permanently adhere to the personal image.
A lightly cancelled stamp would have the postmark on a corner or small portion of the stamp. As lightly cancelled stamps are in general more valuable than heavily-cancelled (exceptions, discussed below, may be bulls-eye cancellations and special or rare postmarks), collectors have at times rubber-stamped (or handwritten) "philatelic mail" or the like on their covers to get the postal clerk or mail processor to cancel the stamps lightly. (It was perhaps from concern that a conventional cancellation device would damage some of Tonga's early foil stamps that a rolling cancellation device was employed.)
A bulls-eye cancellation is a readable postmark which entirely or almost entirely is on the postage stamp. They are favored by stamp collectors because one can see the time, date, and location where the stamp was used. The prevalence of bulls-eye cancellations varies considerably by country and time period.
Cancellations may either be applied by hand or machine. Hand cancellation is often used when sending unusually shaped mail or formal mail (e.g., wedding invitations) to avoid damage caused by machine cancellation.
The United States Postal Service regulations prohibit the use of slogans or pictorial material in regular hand-stamped cancellations (whether with or without killer bars).
First day of issue of a stamp or piece of postal stationery is another type of cancellation.
There are railway post office cancels, ship cancels, and highway post office cancels.
In the United States, while cancellations are nearly universally applied by the authority of the United States Postal Service, it is legally possible to use one's own cancellations on a letter bearing United States postage stamps — if the letter is delivered by the sender, its employee (in the case of a company) or by a private delivery service following the requirements of the "Private Express Statutes". Private cancellations have also been used in the context of local posts and applied to artistamps by their makers. Private cancellations have actually been used in Germany. Private cancellations are to be distinguished from private overprints.
In the United States a distinction is drawn between special cancellations, in which the killer is a slogan, usually encased in a rectangular box, and pictorial cancellations. There are regulations pertaining the special cancellations.
The term "pictorial cancellation" is sometimes used, loosely and perhaps technically incorrectly, for slogan cancellations, which contain some sort of commemorative phrase in addition to the regular format of the cancellation.
In the United States, official pictorial cancellations are almost invariably applied at special "stations" (post offices existing only for a limited time, usually one day, at special events), although there are frequently other pictorial cancellations that are not officially described as such — they are among what are called special cancellations and are special die-hubs added to machine cancels, which usually contain merely a slogan but sometimes contain a picture. There are a very few exceptions in which a particular post office uses a pictorial cancellation on all its mail. The range of allowable subjects is very broad, and may include a variety of commercial tie-ins, such as to movie characters. There has been a change, however, and what were formerly referred to as "pictorial cancellations" are now frequently called "pictorial postmarks".
Pictorial cancellations may, though more commonly in other countries than in the United States, form the day-to-day cancellation of a station. For example, there are a number of permanent pictorial postmarks in India and Great Britain.
In Japan there are several different types of what are there called "special postmarks":