Contemporary design tends toward minimalist aesthetics, emphasizing clean lines, open spaces, and subtle ornamentation. Working from the basic philosophy that less is more, contemporary styling avoids ostentatious display or unnecessary accents, and is built so that form emphasizes function.
Traditional design is a broad umbrella term covering any design styling coming out of historical European fashions. Traditional design can be evocative of anything from Renaissance to Victorian aesthetics, and may feature elaborate ornamentation. Traditional design tends toward richness in color, accents, and upholstery.
Transitional is intended to serve as a midpoint between traditional and contemporary design. Neither as ornate as traditional styles nor as severe and minimalist as contemporary style, transitional design features more curved lines, simplicity, and a focus on comfort, active function, and less chrome and glass than you would find in modern design.
Modern design style is adventurous and original. A catchall term for a wide variety of styles, modern styling is creative and unexpected. It tends toward simple forms and unconventional shapes.