# What does alpha in smoothing stand for

I want to apply Gaussian smoothing to a dataset and came across the smth.gaussian function in R. That besides the numerical input data requires two parameters:

window : the length of the smoothing window, if an integer, represents number of items, else, if a value between 0 and 1, represents the proportion of the input vector

alpha : parameter to determine the breadth of the gaussian window, yielding more or less sensitive smoothing characteristics

According to this explanation window tells where smoothing has to be applied whereas alpha tells how much smoothing has to be applied. However I don't know how I should actually interpret this alpha. For example what does it say when alpha = 0.5 or alpha = 10? In addition, what is the upper boundary of this alpha value?