The term "carbine" is relative and must be viewed in the historic context in which it is used.
Back in the days when the British line infantryman was armed Brown Bess Musket, the barrel was 39" long (that's the 2nd model Brown Bess as opposed to the 42" long First Model) and a light infantry carbine could be 32" long.
In the 1860s, when the regular British Infantryman was armed with the Enfield rifle (39" barrel), sergeants and riflemen (60th Regt & 95th) were armed with a 33" short barrel Enfield. Calvary received a 24" Enfield Musketoon. All were the same gun, just different barrel lengths.
In World War I, when Germany armed her troops with the Mauser 98 with a 29" barrel, their carbine was a mere 24" long. During the same time frame, our 1917 Enfield rifle had a 26" barrel and our 1903A3 Springfield a 24" barrel. Both 1917 and 1903A3 were considered rifles by our military.
Modernly, and you have the concept, the carbine is a shortened version of the rifle. Whereas the normal M16 has a 20" barrel, the M4 has a 14.5" barrel.
------------------
Vigilantibus et non dormientibus jura subveniunt