Ascendant
Also called Rising sign, ASC
The degree of the ecliptic rising over the eastern horizon at your moment of birth.
The Ascendant starts the first house, and the rest of the houses follow from it. It is the most time-sensitive point in the chart: a degree every four minutes, a whole sign every two hours.
Often glossed as "how you come across". Technically it is simply an angle set by time and latitude — two people born the same day two hours apart can have entirely different Ascendants and identical Sun signs. Which is exactly why Sun-sign-only descriptions are so broad.