Altraiding is the act of either using an additional, "alternate" Minecraft account to raid other nations. Usually, this act is done in order to benefit one nation or to destroy an opponent nation without suffering the consequences of conflict. The act of altraiding usually brings the international community to denounce your community and actions, and at times can result in outward conflict or attacks on the host nation. Therefore, its often advised that nations do not altraid at all, or to ascribe to a level of upmost secrecy. This is different than having combat alts, but not exclusive, as combat alts can be used to raid an enemy nation.
Notable altraiding incidents
BobbySwan raiding Kraken