What is the HBA card?

HBA: Host adapter, or Host bus adapter is a circuit  board which  connects a computer, which acts as the host system, to other network and storage devices.

A HBA (host bus adapter) is an integrated circuit adapter or circuit board that is designed to provide physical connectivity between a computer host and storage devices or a network.

HBA is the Host Bus Adapter. It is the Fibre Channel equivalent of an NIC (Network Interface Card) with the exception that an HBA essentially "extends" the Server Bus outside of the physical hardware (or atleast makes it look appear this way to the OS). This way the whole Storage Area Network (SAN) looks and acts like local disks to the OS (with some exceptions). Easy way to remember: Fibre Channel EXTENDS the Bus, hence the name Fibre CHANNEL...channel = bus. A lot more to say about Fibre Channel, but I hope this little bit helps.

It's a host bus adapter that provides input output processing and physical connectivity between servers or network devices

Host Bus Adapter. For Faster Communications which directly connects to PCI slot of server

An HBA is a hardware device, such as a circuit board or integrated circuit adapter, that provides I/O processing and physical connectivity between a host system, such as a server, and a storage device. The HBA transmits data between the host device and the storage system in a SAN and relieves the host microprocessor of the tasks of storing data and retrieving data. The result? Improved server performance.

SCSI host bus adapter (a 16-bit ISA card) In computer hardware, a host controller, host adapter, or host bus adapter (HBA) connects a computer, which acts as the host system, to other network and storage devices. The terms are primarily used to refer to devices for connecting SCSI, Fibre Channel and eSATA devices.

Thanks 

Many good answers here, nothing to add

 

Regard. 

https://en.m.wikipedia.org/wiki/Host_adapter

HBA (host bus adapter) is used in server to connect the server to SAN (storage area network).