In terms of Computer, ISA - Industry Standard Architecture
Industry Standards Architecture is a computer bus standard developed for the earlier generation of IBM PCs. The protocol was developed in the early 1980s by a team led by Mark Dean at IBM.
In terms of steel angles, ISA - Indian Standard equal/unequal Angle
ISA angles are rolled steel angles that are made with Indian standards and comes in different grades on the basis of size, thickness, area and weight.
In DBMS, ISA - "is-a"
The ISA (pronounced as "is-a") relationship is most frequently used to represent generalization and specialization in an ER Diagram. It is used in situations when an entity type contains certain entities that has special properties not shared by all the entities. Then, those two entities will be represented by a "ISA" relationship between them.