civil twilight
Astronomical term for the period when the sun is just below the horizon and there is still enough natural light for most outdoor activities without artificial lighting.
During civil twilight, you can still read a book outside without streetlights.
薄明 is a general term for twilight or dim light, while 常用薄明 specifically refers to civil twilight, a defined astronomical phase.
航海薄明 (nautical twilight) is the next phase after civil twilight, when the sun is lower and the horizon is still visible at sea.
天文薄明 (astronomical twilight) is the darkest twilight phase, when the sun is 12–18 degrees below the horizon and the sky is dark enough for most astronomical observations.
Compound of 常用 (じょうよう, 'everyday use, common') and 薄明 (はくめい, 'twilight, dim light'). The term is a direct translation of the English 'civil twilight', where 'civil' refers to civilian activities.