asynchronous online materials

I was looking at applying to the bristol chemical physics degree and it says some learning will be asynchronous online materials, what exactly does it mean by this? and does anyone know how much time will be doing this ?
the link is
Unit and programme catalogues | University of Bristol
if it helps

The page you mention includes "asynchronous online materials, including narrated presentations and worked examples"

That sounds like it might include video presentations -- e.g. something similar to Youtube videos.