What is a Pergola?
An archway in a garden or park consisting of a framework covered with trained climbing or trailing plants.

What is the difference between a gazebo and a pergola?
A gazebo is a free standing structure with a peaked roof. It usually is a polygon with 6 or 8 sides, or it’s round. It can be just an open framework or it can have a proper roof on it. On the other hand a pergola is either a free standing framework structure or it’s attached to the side of an existing structure. It has columns that support cross beams, which support perpendicular joists on top of that. These are then usually topped with additional slats for partial shading.