Excellence is a talent or quality which is unusually good and so surpasses ordinary standards. It is also used as a standard of performance as measured e.g. through economic indicators.
Excellence is a continuously moving target that can be pursued through actions of integrity, being frontrunner in terms of products / services provided that are reliable and safe for the intended users, meeting all obligations and continually learning and improving in all spheres to pursue the moving target.
In modern public relations and marketing, "excellence" is a much overused buzzword that tries to convey a good impression often without imparting any concrete information (e.g. "center for excellence in ...", "business excellence", etc.).