The houses are what we may call the earthly Zodiac: the same cycle that happens in space repeats itself on Earth, and consequently in human experience, corresponding to the sectors of life.
There are 12 sectors in direct analogy with the signs of the zodiac. House 1 is analogous to Aries (beginnings), house 2 to Taurus (stability), house 3 to Gemini (adaptation), and so it continues.
In short, the astrological houses are the sectors of life where the astrological influences of the planets, signs and aspects take place.
The most important houses are the angular houses, or the cardinal points of life:
The beginning of this house (the cusp) is called the ascendant (Asc)
The beginning of this house (the cusp) is called the Nadir or bottom of the sky (IC or Imum Coeli)
The beginning of this house (the cusp) is called the descendant
The beginning of this house (the cusp) is called the Midheaven (MC or Medium Coeli)