GIS is a Geographical Information System. It is integration of hardware, software and data for capturing, managing & analyzing information. This is one of the ways maritime traffic is monitored and analyzed. Safety and security have one of the highest priority in maritime industry. GIS allows to understand, interpret & visualize data better.

Ashore GIS can be viewed in three ways:

1. The Database View: A GIS is a unique kind of database of the world—a geographic database (geodatabase). It is an "Information System for Geography." Fundamentally, a GIS is based on a structured database that describes the world in geographic terms.
   
   
2. The Map View: A GIS is a set of intelligent maps and other views that show features and feature relationships on the earth's surface. Maps of the underlying geographic information can be constructed and used as "windows into the database" to support queries, analysis, and editing of the information.
   
   
3. The Model View: A GIS is a set of information transformation tools that derive new geographic datasets from existing datasets. These geoprocessing functions take information from existing datasets, apply analytic functions, and write results into new derived datasets.

Here is a little info about GIS from wikipedia

A geographic information system (GIS), also known as a geographical information system or geospatial information system, is any system for capturing, storing, analyzing, managing and presenting data and associated attributes which are spatially referenced to Earth.

In the strictest sense, it is any information system capable of integrating, storing, editing, analyzing, sharing, and displaying geographically referenced information. In a more generic sense, GIS is a tool that allows users to create interactive queries (user created searches), analyze the spatial information, edit data, maps, and present the results of all these operations. Geographic information science is the science underlying the geographic concepts, applications and systems.

Is GIS  different from GPS?

Yes they both are different though closely related.

GIS (Geographic Information Systems) is tool to display and analyze information geographically. GPS (Global Positioning Systems) is a technology that uses satellites to give one its position on the Earth with the aid of a GPS device or unit. GPS can be incorporated into GIS by using a GPS device to collect points, lines, or polygons, which can be imported into a GIS application for future analysis and interpretation.