LibreOffice for Windows x86_64

I’d like to understand the difference between LO for Windows vs. LO for Windows x86_64.
Downloading the first I get LibreOffice_5.1.1_Win_x64.msi, downloading the latter I get LibreOffice_5.1.1_Win_x86.msi.
I thought that x86 is for 32bit.
Having on my PC Win 8.1 x64 which one has to be installed?
Thanks

You can install either, they will both run fine on Win 8.1 x64. The x64 LO is available since version 5.0. I’m still running the x86 versions on Win7 x64, the x64 supposed to be faster on x64 OS but I can not confirm this.

x64 is more stable and faster. x64 if used correctly is also way more secure.