1. What are vertical Angles?

Pairs of angles formed where two lines intersect. These angles are formed by rays pointing in opposite directions, and they are congruent. Vertical angles come in pairs.

2. What is midpoint?

The point on a segment that lies exactly halfway from each end of the segment. The distance from the endpoint of a segment to its midpoint is half the length of the whole segment.

3. Tell me what is chord?

a line segment connecting two points on a circle; not "do re mi"
A line segment whose endpoints are both on a circle. Not a collection of musical notes.
Any segment from one point on a circle to another. Despite what you might think, they aren't all that musical.

4. What is parallel Postulate?

A postulate which states that given a point not located on a line, exactly one line passes through the point that is parallel to original line.

5. What is common Denominator?

the bottom part of fractions; in this case when more than one fraction has the same bottom as all the others

6. What is degree?

A unit of measure for the size of an angle. One full rotation is equal to 360 degrees. A right angle is 90 degrees. One degree equals radians.

angles that share a side
Two angles that share both a side and a vertex. They stick by each other through and through.

8. What are complementary Angles?

Angles that add up to 90°
Two wrongs don't make a right, but two complementary angles do. They're two angles that add up to 90° exactly.
Two angles that add up to 90°. Two wrongs don't make a right, but two complementary angles sure do.

9. What is angle Bisector?

A ray that shares a common vertex with an angle, lies within the interior of that angle, and creates two new angles of equal measure.

10. What is angle Trisector?

A ray, one of a pair, that shares a common vertex with an angle, lies within the interior of that angle, and creates, with its partner, three new angles of equal measure. Angle trisectors come in pairs.