This means it should be grown in a pot of some kind and not allowed to grow freely in the ground. Rosemary may grow as a perennial for you, but I wouldn't count on it. If it does, enjoy it. If it doesn't, just plant a new one next year. That's life, buy inexpensive small plants.
Some herbs are biennials.
This means they grow for a season, live through the winter and flower the second season. After flowering, they die. For example, parsley is a biennial. Italian or flat leaf parsley tastes more strongly of parsley than the curly leafed type, but the curly leafed type looks tidier in the garden. Take your pick.