Module is an executable file (ususlly EXE or DLL) loaded into memory. OllyDbg keeps list of loaded modules in a table of sorted data consisting of elements of type t_module. You can receive pointer to table of modules by calling Plugingetvalue(VAL_MODULES) and casting result to (t_table *).
t_module *Findmodule(ulong addr);
t_fixup *Findfixup(t_module *pmod,ulong addr);
char *Finddecode(ulong addr,ulong *psize);
ulong Findfileoffset(t_module *pmod,ulong addr);
int Analysecode(t_module *pmod);