Elements, tags and Attributes
An element in HTML represents some kind of structure or semantics and generally consists of a start tag, content, and an end tag. The following is a paragraph element:
This is the content of the paragraph element.
Tags are used to mark up the start and end of an HTML element.
A start tag consists of an opening angle bracket (<) followed by the element name, zero or more space separated attribute/value pairs, and a closing angle bracket (>).
A start tag with no attributes:
A start tag with an attribute:
End tags consist of an opening angle bracket followed by a forward slash, the element name, and a closing angle bracket:
There are also some elements that are empty, meaning that they only consist of a single tag and do not have any content. In HTML, such tags look just like opening tags:
The syntax is slightly different in XHTML. Empty elements must either have an end tag or the start tag must end with />. In order to ensure backward compatibility with HTML the most common way of writing empty elements in XHTML is to use minimised tag syntax with a space before the trailing />:
An attribute defines a property for an element, consists of an attribute/value pair, and appears within the element’s start tag. An element’s start tag may contain any number of space separated attribute/value pairs.
The most popular misuse of the term “tag” is referring to alt attributes as “alt tags”. There is no such thing in HTML. Alt is an attribute, not a tag.