The phrase "junior scientists" refers to young or less experienced researchers or scientists who are still learning and developing their skills and knowledge in their respective field of study. Full definition
What are the benefits for junior scientists working in academic drug discovery? (sciencemag.org)
The lessons that she learned as a PhD student have also helped her to mentor junior scientists in her group properly, so they could become more productive and support her company's mission. (nextscientist.com)
There is a dark side, however: This progress has come at the expense of junior scientists. (sciencemag.org)