1NXXXX is an American Standard numbering system used for Semiconductor Devices which in now adopted globally. It is named with Joint Electronic Device Engineering Council (JEDEC) identification number.
1N means Single Junction semiconductor. 2N means Double Junction semiconductor.
1 stands for 1 junction. Since the diode is made by two dissimilar P and N semiconductor types..a junction is formed between them. N stands for semiconductor diode and 4007 is the identification number of that particular diode..