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A segment is part of the line connecting two points. These two points are the endpoints of the segment.

The symbol $\stackrel{¯}{PQ}$consists of two endpoints $P$and $Q$, also all the points between $P$and $Q$.

Since the symbol $\stackrel{¯}{PQ}$has two endpoints, thus the symbol $\stackrel{¯}{PQ}$ represents a segment.

The following figure represents a segment $\stackrel{¯}{PQ}$.

A ray is a part of a line that has one endpoint and goes on infinitely in only one direction.

The symbol $\stackrel{→}{PQ}$consists of one endpoint $P$and$Q$goes on infinitely.

Since the symbol $\stackrel{→}{PQ}$has one endpoint, thus the symbol $\stackrel{→}{PQ}$ represents a ray.

The following figure represents a segment $\stackrel{→}{PQ}$.

A line goes in the infinite direction on both sides, thus a line has no endpoints.

The symbol $\stackrel{↔}{PQ}$consists of no endpoints.

Since the symbol$\stackrel{↔}{PQ}$ has no endpoints, thus the symbol $\stackrel{↔}{PQ}$ represents a ray

The following figure represents a line $\stackrel{↔}{PQ}$.

The length of a line segment can be measured by finding the distance between its two endpoints. It is the path between the two points with a definite length that can be measured.

Here the symbol $PQ$represents the distance between the two endpoints$P$andwidth="14">Qwhich is the length of the segment.

Thus, the symbol$PQ$ represents the length of the segment $\stackrel{¯}{PQ}$ .