In the manpage or internet you can find that you can set restrictions to any user with the pam module: limits
The restrictions can be set for the next items:

* core - limits the core file size (KB)
* data - max data size (KB)
* fsize - maximum filesize (KB)
* memlock - max locked-in-memory address space (KB)
* nofile - max number of open files
* rss - max resident set size (KB)
* stack - max stack size (KB)
* cpu - max CPU time (MIN)
* nproc - max number of processes
* as - address space limit
* maxlogins - max number of logins for this user
* maxsyslogins - max number of logins on system
* priority - the priority to run user process with (negative values boost process priority)
* locks - max locked files (Linux 2.4 and higher)

my question is . . .
what is core file size?
and resident set size?
and stack size?

It's not clear to me what does each item mean. This may be because I don't know very well some kernel things, can anyone helpme??

A core file is a dump of memory to disk, used for debugging problems. The limit on the core file size specifies how much memory to dump. If you don't want "core" files, you can set the limit to 0.

The resident set is the number of pages that that are actually in memory (as opposed to being on swap - non-resident). Limiting the resident size will allow more users to use the system, but will also degrade performance and increase swapping.

The stack is an area of memory used by programs to hold intermediate results and subroutine return information. More details here. If you set the stack size smaller than needed by a program, it will fail.