As a type of road, a boulevard is usually a wide, multi-lane arterial divided thoroughfare, often with an above-average appearance in terms of landscaping and scenery.
However, in many places in the United States, particularly California, the term has been severely distorted by developers who applied it to arterial roads that are not boulevards in the conventional sense. There are many so_called "boulevards" in California which extend into the mountains, and those road segments are narrow, winding, and only two lanes in width.
The term boulevard is also used by some to refer to the division or central reservation in such a road, whether that road is specifically a "boulevard" in the above sense or not. It can consist of anything from a simple thick curb of concrete, to a wide strip of grass, to a thoroughly landscaped space of trees, shrubs, and other foliage; in urban areas, boulevards can also contain public art or memorials. Wide boulevards are also sometimes used as rights-of-way for trams or light rail systems.
Notable Boulevard in Berlin the capital of Germany is Karl-Marx Allee that was built primarly in the 50's in Stalinist Clasicism architecture with decorative buildings.
The Cross Bay Boulevard in the Howard Beach neighborhood of Queens, or Roosevelt Boulevard in the Northeast section of Philadelphia is a typical example of a boulevard.
In Chicago, the boulevard system is a network of wide, planted-median boulevards that winds through the south, west, and north sides of the city and includes a ring of parks.