What is meant by the term "meta-parameter"? Can a definition, informal and/or formal, be provided?
For example, in reduced-rank regression, the rank ($r$) can be referred to as a meta-parameter of the method. For instance, see these notes, which I quote below.
The optimal choice of the rank $r$ will usually be unknown, and is considered as a meta-parameter of the method.
Reference: Reduced-rank regression, by Magne Aldrin (2002) in Encyclopaedia of Environmetrics.