What does the TLS means in /lib/tls directory

[Gavin Li]

After installed RHFC, I got /lib/libc-x.y.z and /lib/tls/libc-x.y.z
/lib/tls/386/libc-x.y.z, What is this TLS means? I assume /lib/tls/386/libc
is used for i386 PC, but when I copied these files to my target system
/lib(not /lib/tls/386),
they don't work.
BTW, Does anyone know how can I only install RHFC3 for i386, not for PII?