What is shorthand property?

Shorthand property is a property made up of individual properties that have a common "addressee". For example properties: font-weight, font-style, font-variant, font-size, font-family, refer to the font. To reduce the size of style sheets and also save some keystrokes as well as bandwidth they can all be specified as one shorthand property font, e.g.:

H1 {font-weight: bold;
font-style: italic;
font-variant: small-caps;
font-size: 160%;
font-family: serif}

can be all shorthanded to a space separated list:

H1 {font: bold italic small-caps 160% serif}

Note: To make things even simpler the line-height property can be specified together with the font-size property:

H1 {font: bold italic small-caps 160%/170% serif}