Header is the section of the file that contains info about structure, units, source, etc of the file. e.g. number of data columns (in data section), units of each, range of the data, associated parameters and so on. Is just an identifier like the first lines in an excel file.

Thanks again (and yes, I've installed J701)
One more question:
For a file with a header (about 50 lines) and the rest is numeric data (maybe a thousand lines), how to read only the first 50 lines (header), or the last 950 (data) in order to process it?

Thanks for your answer.
I meant how to read external files (estructured data) with the data to be used in a J program, and how to write the results to a file.
Thanks again.
By the way, that's very good you'll have a better article about J.

Hi
Could you comment about how to handling files in J?
(There is a lot of information about sintax, verbs, and so on,
but precious little about files).
Thanks in advance