Draw No Bet removes the draw from the equation: pick a side, and a drawn match returns your stake as a void rather than a loss. It is equivalent to the 0.0 Asian handicap and sits between the full 1X2 price (higher odds, draw loses) and double chance (lower odds, draw wins).
DNB suits situations where you fancy a side but respect a real draw risk — tight derbies, cagey away favourites. You can also construct it manually by splitting your stake between the win and the draw in the right proportion, which occasionally beats the packaged DNB price. As always, the packaging is only worth taking when the implied probability is below your estimate of the true chance.
Team priced 2.30 to win, 3.30 the draw. DNB offered at 1.70: implied 58.8% for a market where the win chance (excluding draws) is 100 × 43.5/(43.5+26.3) ≈ 62% — a fair DNB would be ~1.61, so 1.70 carries value.