Access (usually called getter) and mutator (usually called setter) methods are methods specifically designed to allow a program to access or update instance variables of an object, without directly modifying said variables.
These types methods are combined with Visibility Modifiers and are crucial in Information Hiding paradigms.
Examples
See Visibility Modifiers to understand private and public
public class Person
{
private int age;
public void setAge(int newAge) //Mutator Method (changes age)
{
age = newAge;
}
public int getAge() //Accessor method (accesses age)
{
return age;
}
}