| Question | Answer |
| parallel lines | Parallel lines are always the same distance apart, and will never touch. |
| perpendicular lines | Perpendicular lines meet or cross to form right (90 degree) angles. |
| straight angle | Straight angles are also known as straight lines, and measure 180 degrees. |
| acute angle | An acute angle measures more than 0 degrees, but less than 90 degrees. |
| obtuse angle | An obtuse angles measures more than 90 degrees, but less than 180 degrees. |
| right angle | A right angle measures exactly 90 degrees. Right angles are sometimes called "square corners", because they look like the corners of a square or a rectangle. |
| triangle | A triangle is a polygon with exactly three sides and three angles. |
| acute triangle | An acute triangle is a triangle whose three angles are ALL acute angles (less than 90 degrees). |
| obtuse triangle | A triangle with exactly ONE obtuse angle. (More than one obtuse angle would mean the three angles could not add up to 180 degrees.) |
| right triangle | A triangle with exactly ONE right angle. (More than one right angle would mean the three angles could not add up to 180 degrees.) |
| equilateral triangle | A triangle whose three sides are ALL the same length. (Also called an equiangular triangle, because the three angles would also have equal measures.) |
| isosceles triangle | A triangle with two (or three) sides being equal in length. |
| scalene triangle | A triangle whose three sides all have different lengths. |
| quadrilateral | A polygon having exactly four sides and four angles. |
| parallelogram | A quadrilateral whose opposite sides are both congruent (equal in length) and parallel. Rectangles, squares, and rhombuses (rhombi) are all special types of parallelograms. |
| rectangle | A parallelogram whose four angles are all right angles. |
| rhombus | A parallelogram whose four sides are all congruent. |
| square | A parallelogram whose four sides are all congruent (making it also a rhombus) and whose four angles are all right angles (making it a rectangle). |
| trapezoid | A quadrilateral with EXACTLY ONE pair of parallel sides - the other pair is NOT parallel, so a trapezoid is not a parallelogram. |
| pentagon | A polygon with 5 sides and 5 angles. |
| hexagon | A polygon with 6 sides and 6 angles. |
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