Damage Reduction, difference between "or" & "and"?

[Secane]

I noticed that some monsters with multi-DRs list their DR as, for example, "DR/Good and Cold Iron". While others list it as "DR/Good or Cold Iron".

So... what is the difference between the OR and the AND?

Does creatures with DR ___ AND ___, require attacks to have both the listed alignment/material/magical to bypass?

While creatures with DR ___ OR ___, only requires 1 of the listed alignment/material/magical to bypass?

Please help in clarifying this?

[Bearded Ben]

Yes, your understanding of it is correct

[blackbloodtroll]

You seem to have full understanding of the difference between the word "OR", and the word "AND".