Often used in the context of sports or business to describe a streak of good fortune or success. The team has been riding high since winning the championship.
Pro Tip 2/3
Success Related
Implies recent achievements, not just a generally good state. He's riding high after securing a big investment for his company.
Pro Tip 3/3
May Be Fleeting
Can suggest the success is temporary or at a peak, possibly hinting at future uncertainty. She's riding high at the moment, but the industry is very competitive.