There are three basic types of HyperText Markup Language (HTML) list styles. The first is an unordered list, and it is made up of a series of bulleted elements listed vertically in sequence. The second HTML list style is an ordered list and is identical to an unordered list except that, instead of a single type of bullet, each of the list elements is numbered in sequence. The third HTML list style is a definition list that lists an item, followed on the next line or after a wide indentation by its definition. Each HTML list style can be broadly customized through some HTML tags, such as the type tag, or they can be specifically customized through cascading style sheet (CSS) properties.
There are some abilities that each HTML list style shares. They can be nested within each other, meaning an ordered list can have an unordered list as a list element. A list can be customized through CSS so everything from the spacing around each list element to the type of bullet used can be modified to fit a particular design. All HTML lists also can list nearly anything as a list element or definition, including hyperlinks, images, scripts or even graphical user interface (GUI) components such as text fields.
An unordered list is the most basic HTML list style. It is simply an ordered list of elements, with each element beginning on a new line after the previous one. By default, a circular bullet is placed just before each new element, although this image can be changed to another shape or removed altogether.
An ordered list is similar in many aspects to the unordered HTML list style except the bullets are replaced with sequential numbering. The numbers can either be standard decimal, Roman numerals, letters or a variety of other numbering systems from different languages. When ordered lists are nested, the numbering for the nested lists can be changed, causing the list to appear more like a traditional structured outline. Like unordered lists, the leading numbers also can be disabled.
The final type of HTML list style is known as a definition list. Each element of this kind of list is made from two elements — the term and the definition. The term is the word that will be defined and is the first item displayed in the list element. The definition is generally a sentence or other element that somehow explains, or is related to, the term. The definition can either be rendered next to the term, on the same line but spaced far apart, or it can be rendered on the next line down and indented, which is the default behavior. A definition list can be customized with CSS properties, but it does not contain an area for bullets to be displayed.