Yeah, Zigbee signal repeater or Zigbee extender is just a layman’s term for a dedicated Zigbee Router, e.g. a product that in practice serves no other function than to act as a Zigbee Router (ZR) device, (e.i. sold using words that are easily understood by people who is not familiar with Zigbee technical jargon).
More info here → https://www.home-assistant.io/integrations/zha#using-router-devices-to-add-more-devices
…and even more here → Zigbee networks: how to guide for avoiding interference and optimize for getting better range + coverage