The first house
The first house covers the self, the body, the first impression you make before speaking.
Houses are not sectors of the zodiac. They are divisions of the sky as seen from one point on Earth at one moment, which is why they depend on the time and place of birth rather than the date alone.
This means two things in practice. Without a birth time the houses cannot be trusted, and beyond the polar circle they do not exist at all — part of the ecliptic never rises there.
We use the Placidus system, computed by dividing each point's day arc into three equal parts by time.