What does "require" actually mean?

[Patrick O'Callaghan]

I thought I had a working understanding of yum and rpm, until I came
across this:

# rpm -q --whatrequires libvdpau
no package requires libvdpau
# yum --assumeno erase libvdpau
[snip]
Transaction Summary
==============================================================================================================
Remove  1 Package (+147 Dependent packages)
...

Why does yum want to remove 147 additional packages if none of them
require libvdpau? (Note that I'm not asking about libvdpau specifically,
it's just an example).

poc