What is temporal neighborhood?
The temporal neighborhood refers to data nearby in time. That is; data located in the frames just before and just after the current frame.

The spatial neighborhood on the other side refers to the data nearby in space. In this case this is the pixels nearby in the same frame.

Spatio-temporal filters (which is 3D filters) takes both nearby pixels in the current frame and nearby pixels in nearby frames into account. In this way you can take advantage of information from more than one frame, which is often a good idea since most video sequences does not change much from frame to frame.