What does this size mean in css {font: 14px/24px Arial, Helvetica, sans-serif}

Question

What is 14px/24px here? Which is the real font size?

Answer 1

First is font-size the second is line-height

Quote from the specification for font shorthand

'font'
Value: [ [ <'font-style'> || <'font-variant'> || <'font-weight'> ]? <'font-size'> [ / <'line-height'> ]? <'font-family'> ] | caption | icon | menu | message-box | small-caption | status-bar | inherit