What is the term for a string that is made up of fixed-length components?

I have a data string that is defined as having two characters for the ID value, six characters for longitude, etc. "Fixed-length string" does not convey the requirement for internal bits of the string to be fixed-length as well.

The concept comes from punch cards and mechanical readers where field locations had to be set in hardware. It is called a:

fixed length record

A straightforward google search for fixed length record will find you lots of similar definitions.

I would call it "a data string made of fixed-length fields". A bit verbose, but precise enough, I think.

You could call it a data structure.

Or, to be more precise, a data structure that happens to reside within a fixed length string.