What is the difference between a meditation course and a single guided meditation?

A single guided meditation is complete in itself. You open it, practise, and it ends. A course is a sequence with a direction: several sessions that build on each other toward one thing you named at the start. Each session in a course knows which techniques came before it and where it sits in the arc, so a later one deepens what an earlier one introduced rather than starting again. In StillMind a course runs between three and fourteen sessions depending on the type and the length you choose, and you can see the whole sequence, every session named, before you begin.