This should again be obvious, but it isn't. IBM once rated software programmers on how many lines of code they wrote. Microsoft remembered that customers don't buy software by lines of code, they buy it for what it can do. The travel agency doesn't make money by talking with X customers per hour. The book will later discuss internal and external customers.
External customers buy our goods or services.
Most people in large companies, however, rarely see an external customer. Instead, they provide goods or services to other people in the company. These are internal customers. Manufacturing is engineering's customer. Know what position you play on the team, and accept your position.