What does “senior graduate student” mean in this context? I am an Indian student enrolled in an integrated master’s-of-science program and currently in my fifth (final) year of the program. So should I be called a senior graduate student or senior undergraduate student?

[Edit]: I read this https://www.numfocus.org/programs/john-hunter-technology-fellowship/ on the first line of second paragraph.
I quote that here:


  The program consists of a 6 month project-based training program for postdoctoral scientists or senior graduate students.


Also the eligibility is:


  Eligibility: Eligible applicants are postdoctoral scientists or senior PhD students, or have equivalent experience in physics, mathematics, engineering, statistics, or a related science.


Am I eligible? I am an Applied Mathematics student (maths major).
When talking about undergraduate studies, "senior" has a specific meaning in the US system, i.e. a student in their last year of a bachelor's degree.  But there isn't a specific meaning in the context of graduate studies; here "senior" just has the generic meaning of "more advanced, more experienced".  Of course, this is relative.

In the context you mention, referring to "postdoctoral scientists or senior PhD students", it seems clear to me that they mean a PhD student who is, at least, in the second half of their studies.  US PhD programs usually involve 2-3 years of advanced coursework, followed by dissertation research.  This program seems to be intended for students in the research stage, and it will likely expect that the students have a base of advanced knowledge in the relevant subfield.

From your description, I don't think you are eligible for this program.