What's the difference between single domain antibody?

As is known, single domain antibody (sdAb), also known as nanobody, has only one heavy chain variable region domain (VHH), which is the smallest known binding unit of target antigen.

Analysis of single domain antibody immunogenicity is conducive to studying immunogenicity of antibody drugs

More information please refer to https://www.creative-biolabs.com/preciab/reformat-into-vhh.htm.