One locus impacting a diversity of characters.
Given pleiotropy a mutation can result in a change in many traits rather than in just one. This concept of pleiotropy can be envisioned as being a consequence of a affecting more than one metabolic pathways and/ore many different tissues so that changes to the encoding gene results in a diversity of effects.
An additional though still related interpretation of the concept of pleiotropy is seen with the idea of antagonistic pleiotropy.
Normally pleiotropies are either fairly rare or require that one look closely at phenotype to discover a diversity of subtle changes. These tendencies probably reflect how changes in genes that impact too many different systems in the body are more likely to have negative rather than positive impacts and therefore would either be if substantially mutated or otherwise less likely to be retained by natural selection.