What is my bike frame .    What are those numbers on my bike frame?
The numbers that are often punched into steel and aluminium frames below the bottom bracket are a serial or identifying number. You may have a look at Wikipedia for an explanation what a serial number is.

If you know the make and model of your bike the number may help to identify your bike after it was stolen and recovered. For example: "This 1996 Giant TCR is my bike and not just any of thousands of Giant TCRs because it has the very frame number I provided to police when reporting the theft." It is therefore prudent to note the number.

With the exception of rare hand-built frames it has no other use.