In general, an attribute is a characteristic. In HTML, an attribute is a characteristic of a page element, such as font size or color. Attributes are used to amplify a tag. When a Web browser interprets an HTML tag, it will also look for its attributes so that it can display the Web page's elements properly.
Techopedia explains Attribute
Attributes provide additional information about HTML elements. For example, HTML links are defined by the a tag. The link address is specified in the "href" attribute. Note that HTML attributes are always enclosed in quotes.
HTML attributes have a few key characteristics:
Attributes provide more information about HTML elements
Attributes are always specified in the start tag
Attributes are presented in name/value pairs such as: name=value
This definition was written in the context of HTML