Need to improve my knowledge...

Hi,
ok I am very close to buy a 360 for about 350$. The engine is stock and running, with all gaskets replaced.
The only thing is that the guy told me that one of the lifter was unloading, and that at startup the engine "clack" for a couple of minutes then it is ok.

So, I would appreciate if someone could explain me, what is a lifter that is unloading? :scratch:
How bad is that kind of problem?
Is it a lot of $$$ to fix normally?

Thanks again