Most of the Internet sites I checked, including Grammar Girl, seem to define the 2nd person POV as writing using the second person verb tense.
In the Second-Person Point of View: Give Your Story a New Perspective by Tal Valante the 2nd Person POV is described as: In fiction, pure second-person POV uses the perspective of a single character, the protagonist, to tell the story. This character is well-defined, with habits and traits and a unique personality. The reader is simply placed "behind" this character, seeing and experiencing the world through his eyes, body and mind.
Personally, I view Valante's description as writing in the 1st Person POV.
Some time back, I found an article, but cannot recall where, that led me to believe 2nd Person POV is: You, the author, are relating a conversation between two people. One person is your story's narrator and the second person is telling the story to your narrator. For example, assume that in your story, the narrator, Tom, is telling your reader about a story he has been told by a second person, Bob. At the start of the conversation, Tom is not aware of the story's content. Since the story content being related has already happened, you the writer can have Bob relate the story using the First Person, Third Person Limited, or Third Person Omniscient POV. As the story unfolds, Tom can only relate, to your reader, what Bob tells him. However, as the writer, you can have Tom interrupt Bob to ask a question or to gain further insight into something Bob said. In this sense, Tom is using the First Person POV. Based on how much you the writer want Bob to know about the story, Bob can use any of three POVs listed.
How do you define the 2nd person POV?
updated to add to example.