Consecutive Interior Angles
In the figure
below, angles 4 and 6 are consecutive interior angles. So are angles
3 and 5.
Consecutive interior angles are supplementary. Formally, consecutive
interior angles may be defined as two interior
angles lying on
the same side of the transversal cutting across two parallel
lines.
Parallel lines cut
by a transversal 

See
also
Alternate
interior angles, alternate exterior
angles
