Summer solstice

The summer solstice is when the Sun is at its highest point in the sky during a year. The solstice itself is one moment, but many use the word to mean the day when the solstice happens. The summer solstice does not always happen on exactly the same day.
The word solstice comes from Latin and means that "the Sun stands still". 
For the northern hemisphere, the summer solstice is around 21 June (20, 21 or 22 of June). This means that the sun is at the northern tropic. For the southern hemisphere, the summer solstice is around 21 December. This means that the sun is at the southern tropic.