What do R_X86_64_32S and R_X86_64_64 relocation mean?

Got the following error when I tried to compile a C application in 64-bit FreeBSD:

relocation R_X86_64_32S can not be used when making a shared object; recompile with -fPIC

What is R_X86_64_32S relocation and what is R_X86_64_64?

I've googled about the error, and it's possible causes - It'd be great if anyone could tell what R_X86_64_32S really means.