What does .aspx mean?

the .aspx extension is for standard programing web by Microsoft, it's called ASP.NET, so if you browse in the internet and found .aspx that mean that web have been programing with ASP.NET, different from .php, .php mean standard web programing by open source and also know as PHP (i am forgot what PHP stands for). all i mentioned above are different with .html or .htm. .html or .htm are not using programming language just standard web structure called HTML (Hyper Text Markup Language) it's is a based Language for making a web. Hope that helps, and if you still confusing i'am happy to explain again for you. Sorry if my english are not good, because i am still studying it. Happy myloter my friend

aspx is the extenstion of any webpage. this is of no use at the client side (means at your pc.)
this is used as a recognition by the server as which type of file is this. this is the microsoft web tech extension. there is an IIS webserver which recognise this and run this at the server side, do some data base operation create the html page according to the programming in the page and send to the client with html.

Aspx is extended active server pages. i.e Whenever you entered a request from the aspx page like clicking a button to submit on the page, the following events occurs.

The request is send to the web server on which the .aspx file resides. Then this request is processed by the server and send the output to you(client).

This is a Server-Side computing techique. You can create the .aspx page in the Microsoft visual Studio .NET (framework).