Conversion rate type is the rate type that would be used for conversion.
Conversion is refers to when you enter a foreign currency journal/invoice etc and
the amounts are converted into functional currency.
A rate type is simply a grouping of different exchange rates.
You can enter one exchange rate in one type and another one for the same date in another rate type.
Account type refers to the type of account: Asset, Liability, Equity, Revenue, Expense.
If you could illustrate more on where did you "notice" "Conversion rate type -- Account Type" then
I might be able to shed more light on the topic.