The Midheaven (Medium Coeli, MC) is the point of the zodiac that was culminating above your birthplace at the moment you were born. It marks the cusp of the 10th House — the house of vocation, career, and public reputation.
It is not just "the job": it is the way you position yourself in society, what you seek to accomplish, the direction your life takes toward the outside world. Its sign colors the style of this ambition and this visibility.
The MC is one of the four angles of the chart (along with the Ascendant, the Descendant, and the Imum Coeli). In traditional astrology, planets in conjunction with the MC — or its well-dignified ruler — are powerful indicators of public success, reputation, and authority.
The sign of the MC and its ruler tell us about the nature of the vocation and the means of achieving it. A planet that rules the MC while occupying a strong position in the chart favors a clear and recognized professional path.