A phalanx is a tightly knit group of people or things, like an army troop or a bunch of fans of the same band.
Phalanx refers to any tightly formed group of soldiers or officers, and historically defines a body of Macedonian infantry whose shields overlapped. From that sense, it came to mean any close-knit group. Another definition of phalanx — any bone in a finger or toe — also came out of the military sense: these bones work together closely, just like a military phalanx. The plural for these bones is phalanges, while the plural for the other senses is phalanxes.