This layer is literally the interface between the host (your computer) and the controller (the Bluetooth device).

这一层顾名思义就是主机(计算机)和控制器(蓝牙设备)之间的接口。

youdao

The mobile device can interface directly with an output device using a wired or wireless connection, and can selectively operate as a host or client.

所述移动装置可使用有线或无线连接直接与输出装置介接，且可选择性地作为主机或客户端而操作。

youdao

It also can create a wireless network betwixt digital device. HCI is the interface between software and hardware of Bluetooth module and host.

作为蓝牙模块和主机间的软硬件接口HCI，可对控制基带与链路控制器、链路管理器、状态寄存器等硬件提供统一接口。

youdao

The new 12 Gbps specification will eventually allow the host system to decide how much power a storage device with the interface should use, allowing up 25 W. It will also allow atomic writes, which will improve system performance as well as providing more resilient system designs.

FORBES: Speedy Ways to Move Enterprise Data