What is the 'lagging strand' in DNA replication, and how is it different from the 'leading strand'?

The lagging strand in DNA replication is the strand of the double-stranded DNA molecule that has to be synthesised discontinuously. This is because the two strands of DNA molecules are antiparallel, so run in opposite directions. DNA polymerase can only polymerise DNA nucleotides in a 5' to 3' direction, so can only use a template strand that runs in a 3' to 5' direction. The DNA strand that runs in this direction is synthesised continuously, but the other DNA strand must be synthesised in Okazaki fragments joined with the help of DNA ligase and DNA polymerase 1 (in prokaryotes).