Definitions (Wikipedia):

 

World Wide Web

The World Wide Web (commonly known as the Web) is a system of interlinked hypertext documents accessed via the Internet. With a web browser, one can view web pages that may contain text, images, videos, and other multimedia and navigate between them via hyperlinks.

Web Page

A web page is a document or information resource that is suitable for the World Wide Web and can be accessed through a web browser and displayed on a monitor or mobile device. This information is usually in HTML or XHTML format, and may provide navigation to other web pages via hypertext links.

The Internet

A global system of interconnected computer networks that use standard Internet protocols to serve billions of users worldwide. It is a network of networks that consists of millions of private, public, academic, business, and government networks, of local to global scope, that are linked by a broad array of electronic, wireless and optical networking technologies.

Browser

A web browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web. An information resource may be a web page, image, video, or other piece of content. Hyperlinks present in resources enable users easily to navigate their browsers to related resources.

Reload or Refresh

A browser menu command that updates the contents of a Web page. In most browsers, the keyboard shortcut is usually Command R (Mac) or Control R (Windows).

View Source

A browser menu command that displays the source code of a web page.

Text Editor

A text editor is a type of program used for editing plain text files such as computer code. Basic text editors are often provided with operating systems.

Document

A computer file that contains text (and possibly markup instructions) using ASCII characters

HTML

HyperText Markup Language (HTML) is the predominant markup language for web pages. HTML is written in the form of HTML elements consisting of tags, enclosed in angle brackets (like <this>). HTML tags most commonly come in pairs like <h1> and </h1>, although some tags, known as empty elements, are unpaired, for example <br />. The first tag in a pair is the opening tag, the second tag is the closing tag. In between these tags web designers add content.

File Suffix

A filename extension is a suffix (separated from the basefilename by a dot) to the name of a computer file applied to indicate the encoding (file format) of its contents or usage.

Monospaced Font

A monospaced font, also called a fixed-pitch or non-proportional font, is a font whose letters and characters each occupy the same amount of horizontal space. This contrasts to variable-width fonts where the letters differ in size from one another.

Plain Text

The purpose of using plain text today is primarily a "lowest common denominator" independence from programs that require special encoding or formatting. Plain text files can be opened, read, and edited with most text editors including Notepad (Windows), edit (DOS), ed, emacs, vi, vim, Gedit or nano (Unix, Linux), SimpleText (Mac OS), or TextEdit (Mac OS X). Other computer programs are also capable of reading and importing plain text. It can also be used for more complex activities like web browsers

ASCII

American Standard Code for Information Interchange. ASCII text is another term for plain text.

ASCII Art

A type of early computer art that used plain text to create images. (Lots more here.)

      ____
     /_ _ \
    ( ")"  )
    ) \=_/( 
   (   _)\_)_
    ) /)___/ \
   ( (( (  \_ \
    ) \\   / `.\
   (__//)  |   \\
   __///_  _\   \\
  /_,/ | \/  \   \\_
       | |   |   /-,|
       | |   |    
       | |  /
       | | /
       ( ( L
       | \\ \
       | | \ |
       |/   \|_
       |\    \(

Markup

A markup language is a modern system for annotating text in a way that is distinguishable from the text itself. The best-known example of a markup language in widespread use today is HyperText Markup Language (HTML)

Tag

In the HTML syntax, most elements are written with a start tag and an end tag, with the content in between. Tags are composed of the name of the element, surrounded by angle brackets. An end tag also has a slash after the opening angle bracket, to distinguish it from the start tag.

Source Code
(or just "Code" or "Source")

In computer science, source code is text written using the format and syntax of the programming language that it is being written in. Such a language is specially designed to facilitate the work of computer programmers, who specify the actions to be performed by a computer or, in the case of HTML source code, a browser.

Tags for Designating HTML Elements:

 

<

Less-than symbol. In math, indicates numeric relationships such as 2<3 (2 is less than 3). In HTML, is used to enclose markup instructions to separate them from content.

>

Greater-than symbol. In math, indicates numeric relationships such as 3>2 (3 is greater than 2). In HTML, is used to separate markup code from content.

/

Forward Slash—a character used in HTML to close or end a section of markup. (For some reason, the forward slash if often incorrectly referred to as a backslash which tilts in the opposite direction: \ )

&nbsp;

Non-breaking space

<strong></strong>

An HTML tag that makes text appear stronger (usually by bolding it)

<em></em>

An HTML tag that makes text appear emphasized (usually by italicizing it)

<head></head>

A "container" within an HTML document that holds several items that shape the web page content but are not directly visible in the browser such as styles, scripts, meta data and the document title.

<title></title>

An HTML tag that defines what will appear in the browser title bar

<body></body>

A "container" within an HTML document that holds the content that is visible in the browser window.

<!--   -->

Comment tags that hide notes or other annotations within the body of an HTML document. Used to organize the HTML code.

<p></p>

Paragraph

<br />

Line break (like a carriage return on a typewriter)

<h1></h1>

HTML heading. Numbered 1 through 6 with 1 being the largest.

<ul></ul>

Unordered (bulleted) list

<ol></ol>

Ordered (numbered or lettered) list

<dl></dl>

Definition list

<li></li>

List item

<hr />

Horizontal rule

CSS Terms:

Selectors

Determine which HTML elements a style will be applied to: p (paragraph), h1 (heading 1), img (image), li (list item) are examples of CSS selectors.

Properties

Determine which style will be applied to a selector: color, font-size, margin, padding, border, width are examples of CSS properties.

Values

Determine the specific setting for the property that you are applying to the selector. For the color property a value might be "red" or #f00. For the margin property a value might be 10px or 5%.

Style Tags

p { padding: 10px }

In this example, the selector p would have the padding property set to a value of 10 pixels.