A program, a routine however you call it is a set of commands that can be written in various 'languages', it is basically a set of commands and rules that when performed will do something. for example you could create a program a simple program to add 2 sets to figures together
ie let a=b+c, this simple command would be the basis used for the first calculators if you like and years down the line we have things like Excel that can perform more complex things when creating spreadsheets. We have programs for pretty much everything these days anyhow that is really simple for it, the code that is written to create the program, some of which have to be compiled, is called the source code or just source.
Oh bother, ask Raz I can't be bothered going into it anymore.