Coffee is slightly acidic but the acidity of coffee depends on a couple of different factors. First of all, one determining factor in regards to coffee acidity is the soil that the coffee bean was grown in. If it was grown in soil that is very acidic then it too will be more acidic in nature. Another factor that determines acidity of coffee is what is added to the coffee itself. Many people prefer milk or creamer in their coffee. This will make it less acidic. Some people also water their coffee down.
Most people prefer a coffee that is slightly more acidic because it has a more rich and robust flavor.
First, when it comes to coffee acidity refers to the roast and variety, not the actual acid content, just like how you can describe wines by their acidity. It describes the sensation the brew gives on the tip of the tongue and/or roof of the mouth. It essentially refers to its bitterness. Without that bitterness coffee tastes flat, but when it is too much it can feel too dry to drink.
In chemical terms, coffee is slightly acidic, but nothing compared to carbonated beverages. It's pH is on average in the range of 5.0.-5.1. which puts it more around neutral than it does acidic. The darker the roasted coffees the less acidic they are.
Coffee is a weak acid. The average pH of black coffee is 5.