What is "zektor"

Zektor is a multi-directional shooter arcade game created by Sega in 1982, which challenges the player to pilot a space ship in a quest to recapture eight cities that have been captured by alien robots. Each city is different with a different name as are the robots. The robots also have speech synthesis so that they can verbally challenge a player to retake the cities they control from them. The first wave takes place on the defense grid.