Relationship between PhD applicant and recommender I am applying for PhD programs and most of them ask for my relationship to my recommenders. Two of my recommenders are my undergrad thesis research advisors, so I just put &quot;thesis research advisor&quot; for those, but I am having trouble describing the last one. 
The third recommender is the PI on a research project I worked on. I only met him a couple times though, and I didn't work directly for him; I worked with one of the grad students. Since the grad student knows me much better, she is helping the PI write my recommendation letter (we thought it would be best to have the PI submit the letter since grad programs usually prefer or require that letters come from professors). 
How would I describe this relationship to the PI? Is &quot;research advisor&quot; still acceptable even though I didn't work with him?
'Research project PI' as in your Question, or maybe 'Research project supervisor'. You seem to want something more distant (less personal) than 'thesis supervisor' The word 'project' implies that distance.
Given that the PI is essentially signing something written by another person, that
distance will likely come through clearly in the letter of recommendation.