\label
\label{key}
A \label
command appearing in ordinary text assigns to
key the number of the current sectional unit; one appearing
inside a numbered environment assigns that number to key.
A key name can consist of any sequence of letters, digits, or punctuation characters. Upper and lowercase letters are distinguished.
To avoid accidentally creating two labels with the same name, it is common to use labels consisting of a prefix and a suffix separated by a colon or period. Some conventionally-used prefixes:
ch
sec
fig
tab
eq
Thus, a label for a figure would look like fig:snark
or
fig.snark
.