These are the instruction set architectures for different type of processors.

x86:

x86 is an instruction set architectures for 32 bit or 16 bit processors. These are used for giving commands to the processors.

As days passed x86 now a days is used to refer 32 bit operating systems.

x64:

Similar to x86 this is the instruction set architectures for the 64bit processors.

Note: Even though 86 in x86 is higher than 64 in x64, we need to note that this is for 32 bit processors. While x64 is for 64bit processors.

While downloading any software do check that you are downloading a correct version of the software according to your operating system. If you are downloading the other one instead of the correct one according to your operating system you might get errors. So It’s highly recommended to check it.