Instructional design can be thought of as:
An instructional designer conducts and considers the results of a needs assessment, principles of adult learning theory, and input from key stakeholders and subject matter experts to design an appropriate learning strategy for a specific audience. Additionally the designer selects an appropriate medium, look and feel for content delivery.
A developer assembles the content (audio, video, graphics, documents, etc.) in a manner prescribed by the instructional designer.
The use of task analysis, discussions, interviews, surveys, and other methods to identify the root cause(s) of a perceived performance, knowledge or skills gap of a specific group of people, and to determine what if any training needs might be effectively met through the use of e-learning.