Is Plagiarizing copying material without permission from the author true or false?

Not quite. Plagiarism is a question of attribution, not permission.

Copying material without the author's permission may be a violation of copyright, but it's not plagiarism if you cite the source of the copied material.

Similarly, unless you indicate the copied material and the original source, it's plagiarism even if you have the author's permission to use it.

There are nuances as well: a parody is probably not plagiarism if it's an obvious parody of a well-known work (having a character in your movie script say "but soft, what light through yonder window breaks?" or "Rosebud" is not really plagiarizing Romeo and Juliet or Citizen Kane, because "everyone knows" that's it's not an original line).