What is a leading strand and a lagging strand?

The leading strand and lagging strand are the two strands at the replication fork, which serve as the templates for DNA replication.

The leading strand is the strand of nascent DNA which is synthesized in the same direction as the growing replication fork. The synthesis of leading strand is continuous.

The lagging strand, on the other hand, is the strand of new DNA whose direction is opposite to the direction of the growing replication fork. Replication of the lagging strand is more complicated than that of the leading strand. It is synthesized in short, separated segments, which are then joined together by DNA ligase to form a continuous DNA strand.