There are three qualities that define an under the radar niche for profitable online courses: 1) It has a specific target audience, 2) It generates search traffic, and 3) The audience is looking for a specific solution. The document then lists the top 10 most profitable under the radar niches according to the company Kajabi, including stress management, creativity, pet care/training, arts and crafts, travel, musical instruments, self-defense, home improvement, beauty/makeup, and photography. Examples of potential online course topics are provided for each niche.