A ledger rod is any rod used for ledgering. An 'Avon' rod should be a rod with an 'Avon action... basically based on the work of Richard Walker (1950's), which culminated in the 'Avon Mk IV action'. 'Avon' refers to an action, not a fast tip action, not an 'all through' action, but a progressive action with a reasonably fast tip ... IMHumbleO. But there will be many others, possibly more learned, that will disagree with my simplification. Then again, these days any rod with a tc of 1.25lb that is being touted for ledgering may be called an 'Avon' rod, if the manufacturer reckons that'll result in increased sales. It a minefield these days... but try any fancied rod out first whenever possible, and always (always) match the rod to the strength of line you intend using.
ATVB