HBA stands for Host Bus Adapter, which is a circuit board or integrated circuit adapter that connects a host system, such as a server, to a storage or network device. An HBA allows a host system and connected storage devices to communicate with each other. It is typically characterized by the interconnect technology it supports, as well as its speed, port count, and system interface. Most HBA cards plug into the Peripheral Component Interconnect Express (PCIe) slots of the host computer, although they might come in other form factors, such as mezzanine cards for blade servers.

HBAs support specific types of devices, such as Serial ATA (SATA), Serial Attached SCSI (SAS), and Fiber Channel. Although the term HBA can apply to a variety of interconnects, it is most commonly used with storage protocols, such as Fibre Channel (FC), Small Computer System Interface (SCSI), and SATA.

The main difference between an HBA and a NIC (Network Interface Card) is the type of storage/switch they connect to. An HBA is used to connect to block-level storage such as Fibre Channel, SATA, or SCSI.

In summary, an HBA is a critical component in a computer system that allows devices to communicate with an operating system and the central processing unit (CPU).