The Sun is one of the strongest and most positive cards in Tarot. In a difficult spread, it brings protection, solutions and help. In a neutral and positive spread, it brings complete joy, happiness and love.
The Sun is a card that mostly speaks of happy relationships. But also, like the World, of achievements and rewards.
The main difference with the World, is that the card of the Sun also speaks of actions to take, of changes and fast renewals.
If only one word should describe the Sun in Tarot, it would be joy.
In the Marseille tradition the Sun is also the card of the ideal couple and harmony.