Line-height is a CSS property that controls the vertical space between lines of text in a block element. It is expressed as a unitless number, a length (like pixels or ems), or a percentage. A higher line-height value increases the space between lines, making text easier to read, while a lower value brings lines closer together. Adjusting line-height can enhance the overall appearance of text on a webpage. For example, a line-height of 1.5 is often recommended for body text, as it provides a comfortable reading experience. Proper line-height contributes to better text legibility and visual harmony in design.