Question

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

Explanation:

In geometry, the notation $\overline{AB}\parallel\overline{DC}$ is used to represent segments. The symbol $\parallel$ indicates parallelism. Since $\overline{AB}$ and $\overline{DC}$ are segments (not lines, as lines are infinite and usually denoted without the over - bar in some contexts when just named, but here the over - bar is for segments), this notation describes two parallel segments.

Answer:

two parallel segments