My question is related to the question "When and why do I have to use "trait" for multinomial multilevel models with MCMCglmm in R?" But in contrast to this question, I don't want to know, how
trait has to be used in
MCMCglmm, but what it means in (bio)statistics. The author of
MCMCglmm, Jarrod Hadfield, is biologist. So what do biologists or biostatisticians commonly mean by this word?
(One example to make clear what I'm looking for: If I would be asking for the meaning of "cluster" in statistical papers about educational research, I would be looking for an explanation like "A cluster is a group, to which multiple observations belong to. For example, many students build a class and this class is then a cluster of students. Data with clusters are often analyzed by multilevel models.")