Definition of customer satisfaction
Satisfaction is as a judgment following a consumption experience - it is the consumer’s judgment that a product provided (or is providing) a pleasurable level of consumption-related fulfillment (adapted from Oliver 1997).
Most research confirms that the confirmation or disconfirmation of pre-consumption expectations is the essential determinant of satisfaction. This means that customers have a certain predicted product performance in mind prior to consumption.
During consumption, customers experience the product performance and compare it to their expected product performance level. Satisfaction judgments are then formed based on this comparison. The resulting judgment is labeled positive disconfirmation if the performance is better than expected, negative disconfirmation if it is worse than expected, and simple confirmation if it is as expected. In short, customers evaluate product performance by comparing what they expected with what they believe they received.
Let us take for instance, an airline passenger David who has bought an economy class ticket from London to Singapore. He paid a premium of £450 for a direct flight rather than one that had a four-hour stopover in Dubai. He had firm expectations that his travel time would be short. Now, imagine that there was a six-hour flight delay and he had to wait these many hours at the airport. He had high expectations as he paid a premium price for high-quality product/ airline and now was deeply disappointed when the product failed to deliver. He was very dissatisfied.
Assume the same scenario, but this time, not only was the flight on time, but David was also upgraded to business class. His expectations were exceeded, and he was highly satisfied. 
Oliver, Richard L. (1997), Satisfaction: A Behavioural Perspective on the Consumer, New York: McGraw Hill.