What are undefined and undeclared variables in JavaScript?

When a variable that hasn't been declared using var, let, or const is attempted to be accessed, the error "undeclared" occurs.

Undefined is the result of a variable being declared with the var, let, or const keywords but not being given a value.

An undefined variable is one that has been declared but has no value.The term "undeclared variable" refers to a variable that is completely absent from the programme