Instructional design is the process of developing materials that are used by learners and instructors during and after a course or curriculum. Materials can be created for instructor-led training, virtual training, a-synchronous training, eLearning, and blended learning.
Each situation is different and calls for a specific set of materials. The trainer may be the instructional designer (ID). Or your team may have dedicated IDs who develop the materials in collaboration with the trainer(s), as well as other subject matter experts (SMEs).