Question

what is a replication fork?

Answer 1

The replication fork is a structure that forms within the nucleus during DNA replication. It is created by helicases, which break the hydrogen bonds holding the two DNA strands together

Answer 2

Some more on the replication fork: you will find a DNA polymerase at the replication fork, adding nucleotides to the growing strand. There will be two forks at each end of a replication bubble where the strands are separated, so if you imagine two "Y" - shaped feature then that's the replication fork.