These two terms are often used interchangeably, though in fact they mean different things. Aroma is the smell of a young wine, and is also used generically when discussing the smell of wine. Bouquet is the smell of a mature wine.
Bouquet embraces the physical and chemical changes that take place as wine ages. These smells are harder to describe than the simple fresh, fruity aromas of young wine. White wines often develop a smell and flavour of honey over time; reds become mellower, and gain depth of smell and flavour.