LaTeX differentiates between references to literature or papers and parts, sections objects of the document itself.
In LaTeX the numbering of parts is not exactly specified on writing. It is done by LaTeX compiler. This confronts the writer of a document with the problem to mention a specific part in the text.
To accommodate this problem LaTeX provides a command to define anchors to parts of interest.
\label{MARKER}
These marker then can be referenced with two commands in the text:
\ref{MARKER} % Reference a specified marker
\pageref{MARKER} % Print the page number the labeled MARKER is on.
The label instruction has to come after or inside a \caption
if it is desired
to anchor on a figure, table or other with a caption.
If it is defined before the caption, the label will pick up the chapter, section
or other as anchor.
After defining a lot of anchors, that possibly also have similar topics and similar markers, an author can loose track of which marker is to use for a reference.
Therefore it is a best practice among LaTeX authors to define the anchors according some patterns, example:
chap:MARKER
↣ Anchor for chapterssec:MARKER
↣ Anchor for sectionssubsec:MARKER
↣ Anchor for sub sectionsfig:MARKER
↣ Anchor for a figuretab:MARKER
↣ Anchor for a tableeq:MARKER
↣ Anchor for equationlst:MARKER
↣ Anchor for a code listingitm:MARKER
↣ Anchor for an enumeration listapp:MARKER
↣ Anchor for an appendix subsection
But these is not enforced an authors are free to choose what suits them best.
Often it is cumbersome to write:
See figure \ref{fig:birds} on page \pageref{fig:birds} to see an example of the
new found species.
To accommodate this there are additional packages:
varioref
hyperref
cleveref