What does "schema" mean?
1. **What is Schema**-  In a relational database, the schema defines the tables, the fields in each table, and the relationships between fields and tables.

Yes, They are related to these 3 words,  "conceptual schema", "physical schema" and "external schema". 


External schema for user views
Conceptual schema integrates external schemata
Internal schema that defines physical storage structures


No, It has no relation with "schema" in cognitive psychology

2. Yes, Schema used in other area also like in- 

Programming &amp; Algorithms -XML Schema , Schema (genetic algorithms) 
Science- Body Schema, Image Schema 
Mathematics- Axiom Schema (related to Mathematical Logic) 

3.  Refer above point 1 &amp; 2