what does the "$ISA" mean in my pam configuration file ,thanks!

["liuruihong" <liuruihong baidu com>]

/etc/pam.d/other

#%PAM-1.0

auth     required       /lib/security/$ISA/pam_deny.so

account  required       /lib/security/$ISA/pam_deny.so

password required       /lib/security/$ISA/pam_deny.so

session  required       /lib/security/$ISA/pam_deny.so

 

what does the "$ISA" mean?