There are two words that we use interchangeably and even the dictionary considers them synonyms but I'd like to challenge us to be more judicious about when we use the word "normal" and when we use the word "average." For both words when we say that x is normal or average we're trying to convey a baseline against which to judge y. However normal and average imply completely different, I might argue opposite, methods of establishing the baseline.
Normal establishes the baseline through a rule. It's objective. Anything that doesn't follow the rule is abnormal.
Average establishes the baseline based on the collection of results. It's subjective. The baseline changes as the results change. Result x could be above or below average but it becomes part of the average when evaluating result y. If we wish to exclude x from the average then we're establishing a rule.
When it comes to software, functionality is generally normal and usage is average. In most cases we define [set rules] about how the software is supposed to work but we never know exactly who will be using it or how. It is quite impossible to set a rule as to who will be using the system. Instead we observe and look for trends and patterns. Be careful though because there is no such thing as an average user and when we create rules based on some composite, mythical person, we are sure to disenfranchise real people.
Normal = Objective. Average = Subjective.