What is the name of a "headless" bolt
According to Hardhat Engineer, the correct term to use is stud bolt.  While a stud bolt frequently (most often?) is used where one end is screwed permanently into a fixed part, like the dictionary says (think of the stud bolts for a cylinder head), it can also apparently refer to a bolt with a nut on each end as shown below
 

I agree that this looks like threaded rod, but I do not think that threaded rod is necessarily designed for the stress encountered in a bolting application.