There are several types of "executable format" Linux can support
The oldest is "a.out" (this is long beard and sandal Unix format)
If the program is not self contained (ie it needs library code) then the normal format is ELF.
However Linux will also load and run self contained image files (it has to otherwise it could never get going to get the library files) and many lightweight "embeded" systems do this if they only run a single main application (such as digital osciloscope or ECG machine or Advertising hording/wall).
For most users they don't care as it is the Linux Loder prog 'ld' that does the heavy lift,