If something is urgent it requires immediate attention or action. If you break your leg, you'll need urgent attention at the hospital — that means the doctors will tend to you without delay.
Urgent comes from the Latin word urgentem, meaning "to press hard, urge." You can see that urgent contains the word urge, meaning "to demand or insist." When you get an urgent message, you need to drop what you're doing to deal with it. An urgent need, like hunger, is a pressing one. If you're a music fan, you might know the song "Urgent" by the band Foreigner. The song's lyrics "make it fast, make it urgent" and its frenetic style help define the word.