I am applying for tenure track /postdoc and I asked two professor to write me a research letter. In some job applications I am asked to describe the relationship with them, and I am not so sure what are the correct words.
The first one is a professor in the university where I obtain the PhD. They are also an expert in the field.
The second one is a world-class expert in my field. I know them personally as we meet in conference over the years and I visited them occasionally.
I did not collaborate with both of them.