We have 3 natural curves in our spine. When there is an excessively deep inward curve of the low back, we often think of that as a swayback. Experts also call an excessive curve in the low back lordosis. But as About.com's guide to back and neck pain Anne Asher explains in What is Swayback?, they are not in total agreement as to what constitutes a swayback as compared to excessive lordosis.
I always thought swayback and excessive lordosis were the same, but Asher reports that some experts make a distinction: "Lordosis is present in swayback, but swayback also has features that lordosis does not. For example, in swayback the hip joints extend and the kyphotic curve of the mid-upper back is excessively long going down the spine.", she says.
Whatever you call it, we are talking about a structural deviation that sets one up for strains, pains, and a host of structural imbalances. Treatment, as Asher says, includes developing good postural habits supported by a strong core. This is part of why Pilates is so good for helping those with back pain. Functional core exercises are our specialty.
To learn much more about swayback - the signs, symptoms and treatment, read: What is Swayback?