Formerly called an init, an extension is a file which loads immediately after the Mac OS boots, adding functionality or customization to the operating system. Often the source of conflicts and/or crashes, but neccessary to make the OS the powerful tool many users demand. Extensions will be eliminated in Mac OS X, replaced by background applications and other implementations.

The few characters appended to a filename that tell a user or application what type of file it is.

The extension can be determined by examining the filename and locating the last occurrence of the period or dot. This is typically the fourth character from the end of the name, and the following characters describe what kind of file it is.

Files ending with .txt, .Txt, .TXT and other variations are all files with Content-Type: text/plain. These ascii text files are readable by any text editor or viewer, such as Windows Notepad or *nix's vi. With *nix, most text files do not have extensions, though.

Some files do not have three character extensions, such as the Joint Photographic Experts Group .jpeg format. These must be shortened to .jpg when saved to a system that runs Windows 3.x or DOS.

Some files have more than one dot, as well. A file called does not have a ".windows.txt" extension, because only the characters after the last dot determine the extension of a file. In this case, the extension is .txt.
Extension, a device used to extend the range of a double bass (contrabass).

The extension is one of several solutions to a problem of most (classical, that is orchestra/Symphony) double bassists, namely that composers require them to play notes deeper than contra E, the normal bottom limit of the instrument.

In the past, this problem was sought alleviated by different tunings, and different numbers of strings on the instruments. Today, there are two choices if one wants to play those really deep notes. One is to play a five string bass, which is hard, cumbersome and just plain difficult. The other is to have an extension fitted to your instrument.

An extension is a device which lengthens the fingerboard (sic!) of the deepest string (tuned normally to E), thus making it a C string. 8)

Extensions come in two kinds: mechanical and fingered. A mechanical extension uses a complex array of springs and levers to press the string down, enabling you to play the notes between E and C. The fingered lets you do the work yourself, but also gives you more control. This can help intonation, sound and speed of playing.

An extension is generally a Good Thing.

In logic, the extension of a predicate is the set of things for which the predicate holds.

For example, the extension of the predicate red is the set of all red things.

In hair terms, an extension is a length of fake hair (or real hair for the very wealthy among us) attached to your own hair, to, well, extend the lenghth of your hair. Hair extensions can also be used to create false dreadlocks.
Extensions can be attached to hair in several different ways: by melting a small part of the fake hair and thus welding it to the hair, by weaving it into the hair... There is another way that I can't remember right now.

Ex*ten"sion (?), n. [L. extensio: cf. F. extension. See Extend, v. t.]


The act of extending or the state of being extended; a stretching out; enlargement in breadth or continuation of length; increase; augmentation; expansion.

2. Physics

That property of a body by which it occupies a portion of space.

3. Logic & Metaph.

Capacity of a concept or general term to include a greater or smaller number of objects; -- correlative of intension.

The law is that the intension of our knowledge is in the inverse ratio of its extension. Sir W. Hamilton.

The extension of [the term] plant is greater than that of geranium, because it includes more objects. Abp. Thomson.

4. Surg.

The operation of stretching a broken bone so as to bring the fragments into the same straight line.

5. Physiol.

The straightening of a limb, in distinction from flexion.

6. Com.

A written engagement on the part of a creditor, allowing a debtor further time to pay a debt.

Counter extension. Surg. See under Counter. -- Extension table, a table so constructed as to be readily extended or contracted in length.


© Webster 1913.

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