Silhouette means the overall outline a garment creates before details, colour or decoration are considered.
Where you will notice it
Silhouette explains why two pieces in the same size can feel entirely different: one may follow the body while another builds volume away from it.
What to examine closely
Stand at a distance and look at shoulder width, waist placement, length, volume and the relationship between top and bottom.
A decision worth making
Silhouette is not a universal quality grade. The same technique or feature can be executed beautifully or poorly, and it can be appropriate in one garment but unnecessary in another.