What is mean by this?

Answer 1

you probably mean the keyword this it is used to point to the instance of the class where its used in

Answer 2

"this" is a keyword in java, used to reference variable to current object.

it can be used for following ways.
1. To refer current class instance variable
2. To invoke current class method/cunstructor.
3. To pass as an argument to method/constructor
4. To return current class instance