Final answer:
The default class for variables inside of blocks refers to their scope; they are typically local variables, meaning they can only be accessed within the block they are declared in and are discarded after the block is exited.
Step-by-step explanation:
The term default class for variables generally refers to the visibility or scope a variable has within a block of code. In many programming languages, variables declared inside a block are local to that block and cannot be accessed outside of it. For example, in the Java programming language, a variable declared within a set of curly braces ({ }) has block scope and is only accessible to the code within that block. This means that once the block of code is exited, the variable is no longer available and is typically discarded by the system. The default class in this context is the local variable.