The term M4 has several meanings:

• The M4 macro processing language.
• The M4 motorway is a major British motorway which runs from Chiswick, west of London, into Wales.
• The M4 is also a motorway in Sydney, Australia, running from the western suburb of Emu Plains to the inner western suburb of Strathfield.
• The M4 is also a motorway in the Republic of Ireland, running from the west of Dublin to Kilcock. it is being extended to west of Kinnegad, where the route becomes the N4 and continues to Sligo.
• The M4 Medium Tank is the formal designation of the Sherman tank.
• The M4 Carbine is also a carbine version of the M16 rifle.
• M4 is also Messier object M4, or Messier 4, also known as NGC 6121, a globular cluster in the constellation of Scorpius.
• The Benelli M4 is a shotgun used by the U. S. Armed Forces.
• The Myasishchev M-4 was a bomber used by the Soviet Union.
• The M4 was a more secure version of the Enigma machine used by the nazi U-boat fleet during World War II.
• The M4 missile is the intercountinental thermo-nuclear missile carried by the French Redoutable class submarines. It is capable of more than 4500 km strikes.