Rays 

You can think of a ray as a laser beam.
It begins at one point and continues in one direction. Two
letters are needed to name a ray; one is the point where it begins
and the other is any point that it goes through. The symbol
is the two letters with an arrow on top (as shown in diagram). Notice
that RAY AB IS NOT THE SAME RAY BA. (
is not ). 

RAY ,
consists of the points on segment
and all points C on
such that B is between A and C. You can think of a ray as a
segment that is extended indefinitely in one direction. Rays
have exactly one endpoint and that point is always named first when
naming the ray. 
OPPOSITE
RAY  Any given point on a line determines exactly two rays,
called opposite rays. This point is the common endpoint of
the opposite rays. In the figure below ray PS and ray PQ are
opposite rays, and P is the common endpoint.

Angles: 

ANGLE  An angle
is formed by two rays which begin at the same point (if the two
rays lie on the same line, then it is called a straight angle).
There are several ways of naming angles: a capital
letter at its vertex (
P); a small letter within the angle; a number within the angle,
or by three captial letters, the middle letter is the vertex, the
other two are points on each ray (
SPQ or
QPS). We will often name angles by this last approach.
SIDES
OF THE ANGLE  The two rays that form the angle are called
the sides of the angle. (Side PS & Side PQ)


VERTEX  The common
point for both rays is called the Vertex. (Point P) 

EXTERIOR & INTERIORS
OF ANGLES  An angle separates a plane into THREE distinct
regions, the interior of the angle, the exterior of the angle, and
the angle itself. (The Blue is
the interior angle, and the Yellow is the exterior angle.) 
Angle Addition Postulate 
If R is in the interior of
PQS, then
PQR +
RQS =
PQS.
If
PQR +
RQS =
PQS, then R is in the interior of
PQS.

Acute
Angles 

An ACUTE ANGLE is one
whose measure is LESS THAN 90 DEGREES. Notice
CAB does not quite reach 90 degrees... acute angles are always less
than 90 degrees. 
Right
Angles 

A RIGHT ANGLE is an
angle whose measure is EXACTLY 90 DEGRRES. Right angles are denoted
by a small square in its interior. 
Obtuse
Angles 

An OBTUSE ANGLE is
one whose measure is GREATER THAN 90 AND LESS THAN 180 DEGREES. (This
is a bit different definition from the book  this one is correct) 
Straight
Angles 

A STRAIGHT
ANGLE is one whose measure is EXACTLY 180 DEGREES. A
straight angle is made up of two opposite rays. Another important
fact is that a straight angle forms a straight line. This information
will be used very frequently throughout the year. 
Reflex
Angle 

A REFLEX
ANGLE is one whose measure is GREATER THAN 180 AND LESS THAN
360 DEGREES. 
Congruent
Angle 

CONGRUENT ANGLES 
Two angles that have the same measure are called Congruent Angles.
Equal measure angles are labeled as shown in the diagram. 