Being uncursed is an item property that ensures it has its basic power and effect, usually without extra benefits or penalties. Any item has a 10% chance to be generated blessed or a 10% chance of being cursed, thus 80% of items are generated uncursed. Food items susceptible to rotting can be named as 'slightly rotten' if B/U/C status is unknown.
Most items function well in uncursed state, but some improve drastically when blessed. Consult Blessed page for examples.