URL bar - AbsoluteAstronomy.com

An address bar is a feature in a web browser

Web browser

A web browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web. An information resource is identified by a Uniform Resource Identifier and may be a web page, image, video, or other piece of content...

that either shows the current URL

Uniform Resource Locator

In computing, a uniform resource locator or universal resource locator is a specific character string that constitutes a reference to an Internet resource....

or accepts a typed URL that the user wishes to go to. Most address bars offer a list of suggestions while the address is being typed in. Auto-completion bases its search on the browser history. Browsers have keyboard shortcuts to auto-complete an address, and these are generally configured by the user on a case-by-case basis.

Features

For website
Website
A website, also written as Web site, web site, or simply site, is a collection of related web pages containing images, videos or other digital assets. A website is hosted on at least one web server, accessible via a network such as the Internet or a private local area network through an Internet...

s which use favicon
Favicon
A favicon , also known as a shortcut icon, Web site icon, URL icon, or bookmark icon, is a file containing one small icons, most commonly 16×16 pixels, associated with a particular Web site or Web page...

(a small icon that represents the website), there will also be a small icon in the address bar.
The address bar is also used, in some web browsers, to indicate the security status of the web page. Various colors and padlock icons show if the page is encrypted and how trustworthy the communication is.
In Opera
Opera (web browser)
Opera is a web browser and Internet suite developed by Opera Software with over 200 million users worldwide. The browser handles common Internet-related tasks such as displaying web sites, sending and receiving e-mail messages, managing contacts, chatting on IRC, downloading files via BitTorrent,...

, the address bar can double as a progress bar
Progress bar
A progress bar is a component in a graphical user interface used to convey the progress of a task, such as a download or file transfer. Often, the graphic is accompanied by a textual representation of the progress in a percent format....

that indicates how much of the content of the page has been loaded. This feature was first introduced with Safari
Safari (web browser)
Safari is a web browser developed by Apple Inc. and included with the Mac OS X and iOS operating systems. First released as a public beta on January 7, 2003 on the company's Mac OS X operating system, it became Apple's default browser beginning with Mac OS X v10.3 "Panther". Safari is also the...

, but current versions of the browser no longer exhibit this behaviour.
It can also be used to detect web feed
Web feed
A web feed is a data format used for providing users with frequently updated content. Content distributors syndicate a web feed, thereby allowing users to subscribe to it. Making a collection of web feeds accessible in one spot is known as aggregation, which is performed by an aggregator...

s that can be used to subscribe to pages. Normally indicated by the RSS
RSS
-Mathematics:* Root-sum-square, the square root of the sum of the squares of the elements of a data set* Residual sum of squares in statistics-Technology:* RSS , "Really Simple Syndication" or "Rich Site Summary", a family of web feed formats...

icon "".
It is able to present a Universal edit button
Universal edit button
The Universal Edit Button is a green pencil icon in the address bar of a web browser that indicates whether a web page is editable. It is similar to the orange "broadcast" RSS icon that indicates that there is a web feed available. Clicking the icon opens the edit window...

"" with an extension for the Mozilla Firefox
Mozilla Firefox
Mozilla Firefox is a free and open source web browser descended from the Mozilla Application Suite and managed by Mozilla Corporation. , Firefox is the second most widely used browser, with approximately 25% of worldwide usage share of web browsers...

for editable homepages, e.g. Wiki
Wiki
A wiki is a website that allows the creation and editing of any number of interlinked web pages via a web browser using a simplified markup language or a WYSIWYG text editor. Wikis are typically powered by wiki software and are often used collaboratively by multiple users. Examples include...

s.
The Opera browser is also a Widget engine
Widget engine
In computer software, a widget engine is a software service available to users for running and displaying applets on a graphical user interface, such as that of the desktop.The widget model in widget engines is attractive because of ease of development...

and provides the opportunity for pages to spread their widget by an extra icon "".
In Google Chrome
Google Chrome
Google Chrome is a web browser developed by Google that uses the WebKit layout engine. It was first released as a beta version for Microsoft Windows on September 2, 2008, and the public stable release was on December 11, 2008. The name is derived from the graphical user interface frame, or...

, the address bar (or Omnibox) doubles as a search plugin
Search plugin
A search plugin provides the ability to access a search engine from a web browser, without having to go to the engine's website first.Technically, a search plugin is a small text file that tells the browser what information to send to a search engine and how the results are to be retrieved...

bar which pulls incremental returns
Incremental find
In computing, incremental search, incremental find or real-time suggestions is a user interface interaction method to progressively search for and filter through text. As the user types text, one or more possible matches for the text are found and immediately presented to the user...

for typed phrases or letter combinations from Google Suggest's pre-emptive search. A Firefox addon which duplicates this functionality is available.
Quick searches can, in some browsers, be done by entering the search terms instead of an address. Further a feature known as "keywords" can be used to search specific sites or to quickly get to a bookmarked page. For example with the keyword "w" associated with the Wikipedia search-box you could quickly find an article about cake by entering "w cake" as the address.