Working days not regular days

I called the call centre for my credit card agency yesterday. Turns out my card's due to expire soon and I've not been sent a replacement. The call centre agent was courteous, he checked the information and told me that the card was ready and that the new card would reach me in seven working days. I thanked him and hung up. After hanging up, which is when I get all the insights, I wondered, What does the phrase "working days" mean? Working days for the credit card company? Working days for the government? My company's working days? Why can't they give me the number in regular days, calender days? We'll send you a card in 10 days. Why this unnecessary term which doesn't have a clear meaning? Do you expect me to keep track of the holidays for the bank? Some companies use the phrase "business days". Right. That makes it simpler for the customer. Simplify, people. Use regular days. Do the hard work and give me a number I can understand. Psst -- John Maeda, a professor at MIT, has a wonderful blog on simplicity, Maeda's Simplicity.