"Ultrasonic fingerprint" refers to using sound waves that are of a very high frequency to create a detailed image of a person's fingerprint, which is a unique pattern on their fingertips. Full definition
Most recently, Qualcomm announced its next generation of ultrasonic fingerprint scanners and smartphone manufacturer Vivo demoed the technology in a working prototype handset, which you can see in the GIF above. (androidauthority.com)
However, there is no clear information whether it will be a physical button or the virtual button with ultrasonic fingerprint sensor. (phoneradar.com)
Ice Universe also said that the new chip will power devices with ultrasonic fingerprint scanners embedded into the display. (bgr.com)