Traditionally, astronomers have separated giant planets from brown dwarfs based on the object’s mass. Objects more massive than 13 Jupiter masses but less massive than 80 Jupiter masses are considered to be brown dwarfs. However, in detail, the lower mass threshold is 11 to 16 Jupiter masses depending on the metallicity of the object. This betrays how arbitrary a purely mass-based distinction between planets and brown dwarfs is. Instead, we take a critical look at the population of brown dwarfs for which we have the most fundamental information: transiting brown dwarfs. Transiting brown dwarfs provide us their mass, radius, and sometimes age, which makes them useful for directly testing substellar evolutionary models. Through a better understanding of how well these models describe the population of transiting brown dwarfs, we will develop a better definition of what makes a brown dwarf different than a giant planet: its formation mechanism. It is certainly true that in the mass range spanning between giant planets and low-mass stars that the dominant formation mechanism must change in a significant way. If we can determine which mass or distribution of masses that this change occurs at, then we will have a more physical way to distinguish planets from brown dwarfs. In this talk, we will review how this thesis work has used the TESS mission to contribute 6 new objects to the transiting brown dwarf population and we will examine a few specific examples of transiting brown dwarfs whose masses, radii, and ages have served as useful tests to substellar isochrones.