UUIDs (Universally Unique IDentifiers), also known as GUIDs (Globally Unique IDentifiers) are 128 bit long values that extremely likely to be different from all other UUIDs generated until 3400 A.D.
MADT (multiple APIC description table) entry type 4 (local APIC NMI) has a 2-byte member not at the 2-byte boundary. No idea why that is, the other 24 types are either padded or aligned naturally.