Plagiarizing

1. An act or instance of using or closely imitating the language and thoughts of another author without authorization and the representation of that author's work as one's own, as by not crediting the original author. (Dictionary.com)

2. One example of true plagiarism, that to this day still pisses me off, is the song "Take it off" by Ke$ha. She completely ripped off the old rhyme that my generation, or probably even the older generations sang.
"On the planet Mars
Where the ladies smoke cigars
Every puff they take
Is enough to kill a snake
When the snake is dead
They put roses in their head
When the roses die
They put diamonds in their eye
When the diamonds break
Then it's time to bake a cake
When the cake is done
It is 1981"

3. Songs that sound similar, coincidentally, are the music in California Girls by Katy Perry and Tik Tok by Kesha. They have the same chords and instrumental sounds exactly, the only difference is that Kesha's has more instruments over hers. Even the words sound like they are sung the same in the chorus, they are exactly alike. This is exactly where I heard it from as well, and it's accurate. The guitar and drum are exactly the same and that is my case.