Relational Database Management System, relational referring to relational data (i.e. tables).
Schema Like packages/namespaces, groupings of tables expressing some database logical structure.
SQL implementations There is PostgreSQL is an Enterprise Database like Oracle, SQL Server, but there are others like MySQL/MariaSQL as well as non relational SQL databases (NoSQL).
Candidate Key A column that can uniquely identify a row (or entry) and thus is a potential candidate for a primary key.
Composite Key A primary key consisting of multiple columns.
Primary Key Unique (in that table), non-null candidate key.
Foreign Key A key that points to another primary key of a row (either in another table, or the same).
Multiplicity Refers to the relationship between linked tables. One-to-One (University, President), One-to-Many (University, Students), Many-to-Many (Students, Teachers). In 1:1, FKs will be within same table. 1:many, FKs will be in the other table. many:many, FKs will be in a junction/transition/join/lookup table.
Referential Integrity Enforcing data relationships, changes reflected between foreign keys. No orphans, all child rows must have their parent rows deleted as well.
Domain Integrity Column data is restricted to allowed range of allowed type.
ERD Entity-Relational Diagram