A | B |

Solid | A three-dimensional figure. |

Polygon | A closed plane figure with 3 or more line segments. |

Area | The number of SQUARE UNITS needed to cover a flat surface. |

Line | A straight path that has no endpoints; it goes on and on in both directions. |

Line Segment | The part of a line that has two endpoints. |

Ray | The part of a line that has one endpoint, and goes on and on in one direction. |

Right Angle | An angle that forms a square corner and measures 90 degrees. |

Acute Angle | An angle less than 90 degrees (an angle less than a right angle). |

Obtuse Angle | An angle greater than 90 degrees (an angle greater than a right angle). |

Protractor | An instrument used to measure angles in degrees. |

Circle | A simple closed curve that is named by a point in its center. |

Radius | A line segment from the center to any point on the circle. |

Diameter | A line segment that passes through the center and has its endpoints on the circle. |

Congruent Figures | Figures that have the same shape and size. |

Similar Figures | Figures that have the same shape, but may have different sizes. |

Parallel Lines | Lines that never cross and are the same distance apart. |

Intersecting Lines | Lines that cross each other. |

Perpendicular Lines | Lines that cross each other to form a right angle. |

Face | A flat surface of a three-dimensional, or solid, figure. |

Volume | The measure of the space inside a solid figure. |