Up until the collapse of the Roman Empire, the area that we can call France today was known as Gaul. This was the name given to the region by both the Celts and eventually the Romans that inhabited the area. During the collapse of the Western Roman Empire, Gaul, like many of the former regions once rule by Rome, was subject to a series of invasions from Germanic tribes east of the Rhine. In 486 CE at the battle of Soissons, Frankish armies under command of Clovis I defeated the Gallo-Roman forces in the area which in turn led to the establishment of the Kingdom of the Franks with Clovis I as the first king of the Franks. This new Frankish Kingdom encompassed almost all of the former Roman Gaul except for a few key areas such as Brittany and Septima (although more areas would be added to the Kingdom under Clovis' descendants such as Clotaire, Pepin the Younger, and Charlemagne). The name France as we use today was derived from one of the sub-kingdoms or regnum which at first, was centered around Austrasia a regnum centered along the bank of the Rhine and modern day Belgium which was also reffed to as Francia. Only later did the word Francia come more to describe the area around modern day Paris and eventually the Kingdom Paris was centered in. From here the term Francia evolved into just France.

TL;DR The term for modern day France was Gaul during pre-Roman and Roman times. France is an evolution of the word Francia which came from it's Frankish rulers after they drove out the Romans from former Gaul in the late 5th century.