An angular house is one of houses 1, 4, 7, or 10. The group is named for its relationship to the four principal chart angles: the Ascendant, Imum Coeli, Descendant, and Midheaven.
Astrological traditions often treat angular houses as visible, initiating, or emphasized areas of the chart. That classification is symbolic and varies in application; it is not a measurable form of strength.
House-system details matter because an angle is not always identical to the same numbered cusp. Angular houses are followed by succedent houses and then cadent houses in each quadrant of the house sequence.