What is .Unit in a script I found from developer.roblox.com?

What is .Unit in a script I found from developer.roblox.com?

local direction = attEnd.WorldPosition - attStart.WorldPosition
print(direction)
print(direction.Unit)
I really want to know what .Unit is.
The output:
direction: -16.6207104, 0.000106573105, 0
direction.Unit:  -1, 6.4120668e-06, 0

Spjureeedd have answered the question thank you so much