A roadmap details the features and platforms for future releases over the upcoming months and years. A product roadmap reveals your current plans but is not a commitment. Just like planning a trip, a roadmap communicates in broad strokes what you plan to do.
One normally plans a route for a trip, but rarely follows the route precisely. You may see a restaurant and decide to deviate from your plan to lunch there. You might hear a traffic or weather report and change your route to bypass the problem. You can make corrections to the plan and still make it to your destination.