FName is a combination of a string and a number.
If you have a bunch of objects named “MyObject_1”, “MyObject_2”, “MyObject_3” etc. the “MyObject” part is going to be stored only once. Each name will refer the same string part and will have a unique number part. This is a memory-saving technique which works good given that standard name generation scheme in UE4 uses class name as a string part for an object name and increments the number part.