90 degrees is
1/4 turn
180 degrees
1/2 turn
45 degrees
1/8 turn
270 degrees
3/4 turn
Vertex
the common endpoint of the two rays or segments that form an angle less than 180 degrees. the vertex of 180 degrees angle is any point along the line
Rotation
the movement of a figure a certain number of degrees around a given point sometimes called a turn