LaTeX's standard indexing capabilities (those provided by the makeidx package) only provide for one index in your document; even quite modest documents can be improved by indexes for separate topics.
The multind package provides simple and straightforward
multiple indexing. You tag each \makeindex, \index and
\printindex command with a file name, and indexing commands are
written to (or read from) the name with the appropriate (.idx or
.ind) extension appended. The \printindex command is modified
from the LaTeX standard so that it doesn't create its own chapter
or section heading; you therefore decide what names (or sectioning
level, even) to use for the indexes, and
\indexname is completely ignored.
The index package provides a comprehensive set of indexing
facilities, including a \newindex command that allows the
definition of new styles of index. \newindex takes a 'tag' (for
use in indexing commands), replacements for the .idx and .ind file
extensions, and a title for the index when it's finally printed; it
can also change the item that's being indexed against (for example,
one might have an index of artists referenced by the figure number
where their work is shown).