/usr/lib64 is for 64-bit libraries. /usr/lib is for 32-bit compatibility libraries.

What is lib64 folder?

Are you talking about the /lib64 directory? It should just store 64-bit library files which are loaded by programmes. So it’s the same as /lib, just for 64-bit libraries.

What does lib mean in Linux?

The /lib directory contains kernel modules and those shared library images (the C programming code library) needed to boot the system and run the commands in the root filesystem, ie. by binaries in /bin and /sbin. Libraries are readily identifiable through their filename extension of *. so.