Question

what does the following notation describe?
ab dc
two parallel lines
two parallel segments
two congruent segments

Explanation:

The notation $\overline{AB}$ and $\overline{DC}$ represents line segments (since they have the over - bar which is used for line segments in geometry notation). The symbol $\parallel$ is the symbol for parallel. So, the notation $\overline{AB}\parallel\overline{DC}$ describes the relationship between two line segments.

Answer:

two parallel segments