Front Load dryers are built with the access door located on the front-facing side of your dryer. Frontloaders are characterized by easy access to the interior space and require less work to load and unload.
Top Load dryers are built with the access door located on the top face of your dryer. This common configuration requires less insulation and waterproofing, and is less prone to leaks.
Portable dryers are self contained and are able to be moved into any room with proper fuel hookup points.