Heap tables:
Heap tables are found in memory. They are used for high speed storage on temporary basis. They do not allow BLOB or TEXT fields.
Heap tables do not support AUTO_INCREMENT.
Indexes should be NOT NULL.
Temporary tables:
The temporary tables are used to keep the temporary data. Sometimes it is very useful in cases to keep temporary data. Temporary table is deleted after current client session terminates.
Main differences:
The heap tables are shared among clients while temporary tables are not shared.
Heap tables are just another storage engine, while for temporary tables you need a special privilege (create temporary table).