Balance really is a very complex topic, encompassing so many different elements and areas of physical training. In dog physical skill/fitness training we often see the term "balance" being used mostly in the context of working on unstable surfaces. Where the dog has to put some effort into maintaining his body position while the surface underneath him is wobbling. But this just a tiny little part of balance. The reality is way more complex. Most of the time our dogs need to have good balance during movement! And, as it comes out, not only to stay upright and not fall over…
Link to the Equiosity episode #128 mentioned: https://www.equiosity.com/single-post/episode-128-helene-lawler-pt-2-what-is-balance