Wikipedia says that a massif is "a section of a planet's crust that is demarcated by faults or flexures." It goes on to list mountain-like objects. Is it not true that most mountains are created by faults or flexures? What is it that distinguishes a massif from any other mountain or group of mountains?
My interpretation is that while an individual mountain itself may be part of a mountain range that is marked out by faults and flexures, the actual mountain is demarcated by erosive processes. For example, the Alps in France are a mountain range, demarcated by faults. However, the Matterhorn, shown below, is clearly a mountain figure not marked out by faults or crustal flexing. Instead its prominence from the surrounding regions is caused by the erosion processes of glaciers.
To use the example in the massif Wikipedia article, The Mont Blanc Massif contains peaks within it (Aguille du Midi, the Mont Blanc peak etc., shown below) that are defined by erosion, but the group of these peaks is defined by faulting.