x86-64, AMD64, Intel 64 are some of the other names which represent 64-bit version in computer architecture with x86 instruction set. Here the 64-bit refers to the size of register that is present in the CPU that can access 264 bytes of RAM at a time to perform faster calculations.

It is a representation for 32-bit Intel CPU architecture which has a 32-bit register present inside it. It can access a maximum of  232 of memory address at a time, thus taking more time than 64-bits to perform calculations.

This is a vulnerability which features in OWASP top 10 vulnerabilites. It stands for XML External Entities. XML is  eXtensible Markup Language which is widely used in web applications. This attack takes place when the attacker puts XML parser to parse the input to an unauthorized external entity where external entity refers to a different location other than the intended location and thus allowing attacker to directly get data from that location.