Whats the technical term for a filter that allows a non unity stride when sliding it's window? So a 1D mean filter of size two with a sliding window defined as W below could be considered as having a stride of one.

Wn=(Xn + Xn+1) / 2
Vn=W2n

where as if I were to define a 1D 'stepped mean filter' with a stride of two and labeled U below.

Un= (X2n + X2n+1) / 2

where the number of samples in U (and also V) would be half that of W.
My questions are the following

Is U still a filter (I'm guessing it is even though not fitting with the traditional kernel convolution implementation I associate with filters)
What is the technical language one could use to communicate and research questions regarding filter/non-filter such as just given?
All though not directly related but since I have the floor is, if  V and U would produce equivalent results (my intuition says no)?
That's a decimating filter. As such, it serves as a 1/2-rate resampler.