Today, this specific configuration is most commonly found in legacy environments or as cost-effective lab equipment for CCNA/CCNP Wireless certification studies. In a production environment, it is typically used in a "maintenance mode" where the goal is to keep existing Wi-Fi 5 (802.11ac) infrastructure running until a full migration to Cisco Catalyst 9800 Series controllers can be completed.
AIR-CT5500-K9-8-3-150-0 refers specifically to a software image file ( Cisco 5508 Wireless LAN Controller (WLC) , running version Cisco Community