centroid | the point of concurrency of the medians of a triangle |

circumcenter | the point where the three perpendicular bisectors of the sides of a triangle meet |

circumcircle | a circle that passes through all three vertices of a triangle |

equilateral triangle | a triangle with three equal sides |

incenter | the point of concurrency of the three angle bisectors of a triangle |

incircle | the circle inscribed in a triangle |

medial triangle | the triangle formed by joining the midpoints of the sides of a triangle |

nine point circle | this
circle has its center at the midpoint of the segment joining the
orthocenter and the circumcenter. Its radius is half of the
circumradius of the triangle. The nine points are the 3 midpoints
of the sides of the triangle, the feet of the 3 altitudes of the
triangle, and the midpoints of the segments joining the vertices and
the orthocenter. |

orthic triangle | the triangle formed by joining the feet of the altitudes of a triangle |

orthocenter | the point where the three altitudes of a triangle intersect |

pedal triangle | the
triangle formed by selecting a point in the plane, constructing
perpendicular lines from that point to the three sides of the triangle,
and connecting the feet of those perpendicular lines. |