1. n. The stuff that software writers write, either in source form or after translation by a compiler or assembler. Often used in opposition to “data”, which is the stuff that code operates on. Among hackers this is a mass noun, as in “How much code does it take to do a bubble sort?”, or “The code is loaded at the high end of RAM.” Among scientific programmers it is sometimes a count noun equilvalent to “program”; thus they may speak of “codes” in the plural. Anyone referring to software as “the software codes” is probably a newbie or a suit.
2. v. To write code. In this sense, always refers to source code rather than compiled. “I coded an Emacs clone in two hours!” This verb is a bit of a cultural marker associated with the Unix and minicomputer traditions (and lately Linux); people within that culture prefer v. ‘code’ to v. ‘program’ whereas outside it the reverse is normally true.