A hardtop is a term for a rigid, rather than canvas, automobile

Automobile

An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...

 roof. It has been used in several contexts: detachable hardtops, retractable hardtop roofs, and the so-called pillarless hardtop body style.

Among the modern body designs is the two- or four-door hardtop that typically "does not have a center pillar

Pillar (car)

Pillars are the vertical supports of the greenhouse of an automobile — known respectively as the A, B, C or D-pillar moving in profile view from the front to rear....

" and requires additional reinforcement compared to similar sedan styles for support in rollover

Rollover

A rollover is a type of vehicle accident in which a vehicle tips over onto its side or roof. The most common cause of a rollover is traveling too fast while turning.- Dynamics :Vehicles can roll over in several ways...

 situations.
Before the mid-1920s, 90% of automobiles had open tops, with rudimentary (if any) weather protection provided by a convertible

Convertible

A convertible is a type of automobile in which the roof can retract and fold away having windows which wind-down inside the doors, converting it from an enclosed to an open-air vehicle...

-type canvas top and celluloid

Celluloid

Celluloid is the name of a class of compounds created from nitrocellulose and camphor, plus dyes and other agents. Generally regarded to be the first thermoplastic, it was first created as Parkesine in 1862 and as Xylonite in 1869, before being registered as Celluloid in 1870. Celluloid is...

 or isinglass side curtains.