Ascendent
The Ascendant is the degree of the ecliptic which is rising over the Eastern horizon at the precise time and place of an individual's birth. Put more simply, the Ascendant Sign is the sign of the zodiac which is rising in the East at the moment of birth, and this sign, and the exact position of the Ascending degree, are the starting points in any astrological interpretation.
The Ascendant shows us as we really are - as opposed to the Sun sign which represents our ego and how we would like to be. This is most strikingly obvious if one talks about a person to someone who a casual acquaintance, and describes their character as shown by the Ascendant Sign - in the vast majority of cases, the third person cannot identify those traits as belonging to the subject at all, because Ascendant Sign traits are those that emerge only to those closest to us, and who know us really well.