Based on technical standards for Human Interface Devices (HID), this most likely refers to a "free-form" or "button-free" touch pad implementation

A "HID-compliant" designation ensures that a touch pad can communicate with an operating system (like Windows or Linux) using standard, built-in drivers rather than requiring proprietary software. : Most modern touch pads use the I2C or USB HID protocol "Free" Implementation : In technical papers, "free" often refers to Force-Free (haptic feedback instead of mechanical clicks) or Driver-Free (Plug-and-Play) capabilities. Precision Touchpad (PTP)

A HID-compliant touchpad typically offers the following features and benefits: