Concerning medicine, what are the differences between antibiotics and antibacterials?
An antibacterial is any compound that will kill or at least slow down the growth of strictly bacteria, a domain of prokaryotes.
An antibiotic is often used synonymously, but denotes a compound that kills or slows down the growth of any cellular pathogen, prokaryotic or eukaryotic. So, certain antibiotics can kill bacteria, fungi and parasites but antibiotics have no effect on viruses and prions.
Antibiotics are a broader range of antimicrobial compounds which can act on fungi, bacteria, and other compounds. Although antibacterials come under antibiotics, antibacterials can kill only bacteria.
Penicillin was the first discovered by Alexander Fleming antibiotic and antibacterial.
There are certian classes of compounds which are bacteriostatic, which will not allow bacteria to grow (Ampcillin kills dividing cells) in number.