What are the short fragments of DNA on the lagging strand called?

The short fragments of DNA on the lagging strand are called Okazaki fragments.

DNA polymerase can extend a new strand only in the 5′→3′ direction. Because the two template strands run antiparallel, the leading strand can be copied continuously, while the lagging strand must be built in short sections as the replication fork opens.

Each Okazaki fragment begins with an RNA primer made by primase. DNA polymerase then extends that primer with DNA. Later, enzymes remove the RNA primers, fill the resulting gaps with DNA, and DNA ligase seals the remaining nicks between adjacent fragments.

The fragments were named after Japanese researchers Reiji and Tsuneko Okazaki, whose 1960s experiments in Escherichia coli helped establish that DNA replication is semi-discontinuous. Their work overturned the idea that both new strands were copied continuously. In bacteria, fragments are commonly about 1,000–2,000 nucleotides long; in eukaryotes, they are typically about 100–200 nucleotides. “Primer fragments” and “lagging fragments” are understandable descriptions, but they are not the canonical biological term.