As per definition a rule is a procedure that must be followed, however a policy is more of a guidline. As a quick example
By viewing forum A you accept that you will not spam, if you do you will be banned. This is a rule not a policy
As a general policy being a forum based in the US, we will only provide official support to English posted questions this is a policy, it's not against the rules
If they were to be merged I would like to see it as rules-and-policies