Final answer:
The sign formed with the right hand using a "flat hand" shape that slides up and down the left index finger is called the "B" sign.
Step-by-step explanation:
In sign language, the sign formed with the right hand using a "flat hand" shape that slides up and down your left index finger is called the "B" sign. This sign is made by extending the right hand with all fingers open and flat, and sliding it up and down against the side of the left index finger. This movement represents the letter B in sign language.
Learn more about sign language