Mark Oehlert points to Tom Werner's post Design Shouldn't Always Mean Instructional Design and agrees with Tom that instructional design is different from design.
(By instructional design, I mean a design model that typically prescribes elements such as learning objectives, presentation of information, practice with feedback, and evaluation that ties back to the objectives. There are many instructional design models. A classic one is Gagné’s. A common one is ADDIE - Analysis-Design-Development-Implementation-Evaluation.)
I don't think ADDIE and Gagne are really in the same class. I disagree that ADDIE is an instructional design model. There's nothing in ADDIE about learning objects or the presentation of information. Most e-Learning vendors mention ADDIE or some form thereof on their websites as if it was a real science about creating effective learning.
To me it's an instructional design process -- or even higher level than that , it's a project management approach. You could apply the ADDIE model to software development, right? But there's nothing particularly instructional about ADDIE.
An instructional design model is one that informs the design of the learning experience itself. Whether you use objectives, assessments, exercises. How you motivate and connect with your learner. I consider Gagne's Nine Events of Instruction a model. (Whether or not you agree that it's a good model, well that's a whole 'nother story...)