LaTeX provides a powerful mechanism to deal with cross-references in a document. When writing a document, any part of it can be marked with a label, like ‘\label{mark}’. LaTeX records the current value of a certain counter when a label is defined. Later references to this label (like ‘\ref{mark}’) will produce the recorded value of the counter.
Labels can be used to mark sections, figures, tables, equations, footnotes, items in enumerate lists etc. LaTeX is context sensitive in doing this: A label defined in a figure environment automatically records the figure counter, not the section counter.
Several different environments can share a common counter and therefore
a common label category. For example labels in both equation and
eqnarray environments record the value of the same counter: the
equation counter.