ISD - International Subscriber Dialing
International Subscriber Dialing, also known as International direct dialing (IDD), is the term used to describe an International telephone call made by a person (specially a subscriber) without using an operator. An ISD code has been assigned to each country, so a subscriber need to add this code followed by the individual's phone number to make any International call.
ISD - Instructional Systems Design
Instructional Systems Design is the practice of determining the current state of a learner and then follow some particular instructions to train him more efficiently and effectively.Basically, the practice makes the learning process more effective.