Basicaly it means 'might be, might not be'! If you live in a mild area you might get away with it outside; if you live in a harsher area you might not. It is a cop out term that means very little.

It means plant OK outdoors in summer, but needs shelter in cold weather. However, if you have a sheltered, warm spot in your garden, you might get away with leaving it out all year. Is there a specific plant you're wondering about?

Thank you everso much.
Not really looking at a particular plant as such, just learning about the vocabulary!
So thank you Sheilabub and Bulbaholic!