Excessive dog barking is when a dog continues to disturb the peace by consistently barking non stop whether throughout the day or even throughout the night.
If a neighbors dog does not stop barking during the day or night and continues to bark even if there is a reason for it to bark and the neighbor doesn't do anything to stop the dog barking then they can be fined since there's a noise ordinance including excessive dog barking in some areas.
I love dogs but I do understand that they can disturb some people including myself when they don't stop barking.