(1)Code Behind is code when it is written in separate class file and on other hand CodeInline is written inside an ASP.Net web page.
(2)Code Behind page has extension is .aspx.cs or .aspx.vb and on another hand Code Inline have extension is .aspx only. Code Inline is written inside < script> tag along with the HTML.
(3)Code for all web pages is compiled into a .dll file.