In (very) short, starchart is a software that produce maps of the stars.
For a more in depth explanation, let's quote Startchart's manual by Craig Counterman:
There is a sky. There are things in the sky. This program draws maps of things
in the sky.
The things in the sky include stars, planets, nebulae, clusters of stars, and galaxies. For thousands of years, people have grouped the stars in the sky into patterns, and constellations. More recently, the sky has been divided into areas based on these constellations. For hundreds of years, astronomers have used a latitude-longitude grid for defining the locations of celestial objects. The longitude is usually referred to as right ascension or RA, the latitude is the declination or DEC. Through the year, the sun follows a path in the sky, called the Ecliptic, which is the plane of the earth's orbit. Other planets in the solar system are roughly in this plane.
This program displays all these elements on various display and printer devices.
The locations of stars, nebulae, clusters, and galaxies have been tabulated for hundreds of years. This program uses computerized forms of such databases.
Starchart is intended to produce useful displays on any available device,
and to produce best results on high quality graphics printers, especially those
using PostScript. Output may be captured in files to be edited for especially
customized maps. Comments are included in the output whenever possible to
facilitate this editing. Given a good object-oriented editor, professional quality
maps may be easily produced.
The program has a set of core routines for user interface and data input, while a set of specialized driver routines is provided for each output device.