Shaping
In his book, Science and Human Behavior B.F. Skinner (1953) described shaping by creating an analogy:
"Operant conditioning shapes behavior as a sculptor shapes a lump of clay...The final product seems to have a special unity or integrity of design, but we cannot find a point at which this suddenly appears. In the same sense, an operant is not something which appears full grown in the behavior of the organism. It is the result of a continuous shaping process."
More precisely, shaping is defined as differentially reinforcing successive approximations toward a terminal behavior.
"Operant conditioning shapes behavior as a sculptor shapes a lump of clay...The final product seems to have a special unity or integrity of design, but we cannot find a point at which this suddenly appears. In the same sense, an operant is not something which appears full grown in the behavior of the organism. It is the result of a continuous shaping process."
More precisely, shaping is defined as differentially reinforcing successive approximations toward a terminal behavior.
Example
Jack is a three year old boy with autism. He has limited verbal behavior and his teacher has began a program in which the goal is for him to request an item by saying its name. Jack loves to roll a ball, so she decides to use this interest to teach Jack how to mand (request) by saying ball. She begins by teaching Jack to say the first sound in ball, /b/. When Jack makes the /b/ sound she rolls him the ball and praises him enthusiastically. If he says any other vocalization other than /b/, she does not roll him the ball. After Jack is able to successfully say the sound to request the ball across multiple days, she then increases the difficulty of the task and teaches him to say, "ba" in order to request the ball. If Jack says, "ba" she will roll him the ball. If he gives any other vocalization (including the previous /b/) she does not roll him the ball.
In this example, the teacher is differentially reinforcing Jack by only rolling him the ball (reinforcement) when he pronounces the correct sound, and not rolling him the ball if he gives any other sound (or no sound at all). She is reinforcing successive approximations to the word, "ball" when she rolls it to him for using vocalizations that are closer (sound more like) to the final behavior.
In this example, the teacher is differentially reinforcing Jack by only rolling him the ball (reinforcement) when he pronounces the correct sound, and not rolling him the ball if he gives any other sound (or no sound at all). She is reinforcing successive approximations to the word, "ball" when she rolls it to him for using vocalizations that are closer (sound more like) to the final behavior.