Boulevards of Paris are boulevard

Boulevard

A Boulevard is type of road, usually a wide, multi-lane arterial thoroughfare, divided with a median down the centre, and roadways along each side designed as slow travel and parking lanes and for bicycle and pedestrian usage, often with an above-average quality of landscaping and scenery...

s which form an important part of the urban landscape of Paris

Paris

Paris is the capital and largest city in France, situated on the river Seine, in northern France, at the heart of the Île-de-France region...

. The boulevards were constructed in several phases by central government initiative as infrastructure improvements, but are very much associated with strolling and leisurely enjoyment in the minds of Parisians.

Parisian boulevards and avenues

Avenue (landscape)

__notoc__In landscaping, an avenue or allée is traditionally a straight route with a line of trees or large shrubs running along each, which is used, as its French source venir indicates, to emphasize the "coming to," or arrival at a landscape or architectural feature...

 are usually tree-lined on one or both sides, which is rarely the case for smaller roads.
The Grands Boulevards are essentially 'the best' of the Parisian boulevards.