What is an instance variable?
In object-oriented programming with classes, an instance variable is a variable defined in a class (i.e. a member variable), for which each object of the class has a separate copy. They live in memory for the life of the class.
An instance variable is the opposite of class variable, and it is a special type of instance member. An example of an instance variable is "private double length"
Technically speaking, instance variables are objects stored in individual states in "non-static fields", that is, fields declared without the static keyword. Non-static fields are also known as instance variables because their values are unique to each instance of a class (to each object, in other words); the currentSpeed of one bicycle is independent from the currentSpeed of another.
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You probably mean "instance" variable. It is a variable that is associated with instances of a class. For each instance of a class you create, that variable is also created.