Do you know what is extension of a computer file? It is an indicator to let you know the purpose of the file is. For example, the extension of MS Word document is .doc. If you found that the file extension is .doc, it probably is about MS Word file and it needs MS Word to open it and read it. As the articles published on the web, I would like to give an extension of each article which is .mck. What is .mck stand for? Really need to tell you? …. dot MyCreativeKids. To my dedicated creative kid!