A line that a graph approaches without touching.
Axis of Symmetry
The line over which a graph can be reflected without altering the graph.
A single point at which a function has no value.
If a graph has a horizontal asymptote of y = k, then part of the graph approaches the line y = k without touching it -- y is almost equal to k, but y is never exactly equal to k.
If a graph does not change when reflected over a line or rotated around a point, the graph is symmetric with respect to that line or point.
If a graph has a vertical asymptote of x = h, then part of the graph approaches the line x = h without touching it -- x is almost equal to h, but x is never exactly equal to h.