[Skunkworks] What is the difference between an AP and Wireless Router?

Dear Skunks and Skunkettes, Could someone please explain to me the difference between an AP (Access Point) and Wireless Router? I have done a googling and I am now even more confused than before. I want to buy a wireless router but I have seen some people mention ""wireless router with built in AP" and others say just "wireless router". I want to connect to the internet at least 40 computers in a building with 6 floors and thick walls. So, please friends, explain to me in simple kindergarten english or kiswahili or kikuyu or kimeru...what is the difference between an AP (Access Point) and Wireless Router? Timo.