Taking a glance at the 42 questions tagged with labels at the moment, it seems that they are a weird mixture of questions about labels in diagrams etc. and about the \label
command used for cross-referencing. I propose to embrace the following definition of labels as tag wiki excerpt (and to retag questions to cross-referencing when appropriate):
{labels} is about customizing the labels of diagrams and mathematical constructs like matrices. If your question is about \label or similar commands, use {cross-referencing} instead.