IVR (Interactive Voice Response) is the menu system that greets a caller and routes them based on keypad input. "Thanks for calling Acme. Press 1 for sales, 2 for support, 3 for billing."
IVR can be single-level (one menu) or multi-level (sub-menus, "Press 1 for residential support, 2 for commercial support" after the top-level menu). It can route calls to specific people, hunt groups, voicemail boxes, or external numbers.
Kelir Team Starter includes two-level IVR; Team Pro adds multi-level IVR trees with sub-menus and skill-based routing rules. Recordings can be generated via TTS (text-to-speech, no studio needed) or uploaded.
IVRs are useful for routing inbound demand to the right team. They're not useful for customer-experience theater — long IVR trees with 8 levels are universally hated. Most small businesses use a 3-option top-level menu and call it done.