The word "schema" is simply a contraction (shortened version) of the phrase "schematic diagram"
Schematic diagrams are used in technical situations to illustrate how things put together or how separate parts relate to each other. (example: electrical schematic diagrams show how the many components of an electrical device fit together)
In this topic (Information Systems and Databases) the schema that you should be most familiar with is the E.R.D. (Entity Relationship Diagram) which is a diagram that illustrates how different tables in a relational database relate to each other.
I have attached a sample ERD from:
http://www.sqlnation.com/accessfiles/access_erd.htm
Please note in reply to
cxlxoxk
Database schemas and ERDs are in the 2009 IPT syllabus