The development of instructional materials in a systematic way in order to address the needs of the learner and deliver an effective approach to training. In many cases, this involves using the 'ADDIE model' of instructional theory — analyze, design, develop, implement, and evaluate.
The field of study first emerged in the mid-20th century, and is still influenced by Benjamin Bloom's taxonomy.
More on instructional design:
3 Steps to Creating an Effective Remote Learning Strategy. This playbook is also in presentation format, so you can use it for yourself!