A time of the day when sun is below the horizon between fairly moderate daylight and night darkness causing a captivating view in the Earth' sky which is neither completely lit nor completely dark.

Twilight happens during sunrise in the morning or sunset in the evening.

The morning twilight is known as dawn and the evening twilight is known as dusk.

Why Twilight happens?

Twilight happens when the Sun is directly not visible in the sky but the sunlight still coming is scattered and reflected by the Earth's atmosphere which then illuminates the lower atmosphere.