Nashville sits squarely in what turf people call the transition zone: too hot for cool-season grasses to be comfortable, too cold for warm-season grasses to be reliable. The result is that both grow here, badly advised homeowners run one's calendar on the other, and lawns thin out for reasons that look mysterious.
Tall fescue is the cool-season option and by far the most common in Wilson and Sumner county subdivisions. It stays green through winter, grows hardest in spring and fall, and suffers in July. It grows in clumps rather than spreading, which is why fescue lawns need overseeding to stay thick, and why a bare patch in a fescue lawn will still be bare next year unless somebody puts seed in it.
Bermuda is the warm-season option, common on open sunny acreage and athletic fields. It goes fully dormant and straw-colored after the first hard frost, wakes up in late spring, and grows explosively through the heat that fescue hates. Because it spreads by runners, bermuda repairs its own bare spots, and it almost never needs seed.
The calendars are near-opposites. Fescue gets its most important feeding in fall and should be left alone in the heat. Bermuda gets fed through June, July, and August, and feeding it in November does nothing but grow weeds. Overseed fescue in late summer; overseeding bermuda is usually a waste of money.
Telling them apart is easy in January. If it is green, you have fescue. If it is tan and dormant, you have bermuda. If it is half of each, which is common on lots that were sodded and then patched with seed, you have a management problem, and the honest answer is usually to pick the one that fits your sun exposure and gradually push the lawn toward it.