The Least Publishable Unit is a term from the Publish or Perish school of academic writing. The Least Publishable Unit is the smallest possible kernel of coherent information that can be presented as a paper in the appropriate scientific or academic community. The driving force to segment one's research into LPU's is the natural, rational desire to pad one's resume. Why only have two or three published articles if you can rearrange the material to get five? Everything counts in large amounts. Or small amounts, depending on how you look at it.
Naturally, this phenomenon applies strictly to the academic world. We'd never see anything like that around here.