Plagiarism

According to the Merriam Webster Dictionary, "the act of using another person's words or ideas without giving credit to that person : the act of plagiarizing something" . But in layman's term, It is using someone else's work and claiming that it was yours. Not a respectful nor dignified act especially in arts.
(http://www.merriam-webster.com/dictionary/plagiarism)

Always mention the name of the original creator of the content

Plagiarism is a crime and an insult from the source of what has been plagiarized. Other than that, it is punishable by law. There is such a thing call the "Intellectual Property Code of the Philippines". Here is one particular statement from the Law of Copyright, "178.2. In the case of works of joint authorship, the co-authors shall be the original owners of the copyright and in the absence of agreement, their rights shall be governed by the rules on co-ownership. If, however, a work of joint authorship consists of parts that can be used separately and the author of each part can be identified, the author of each part shall be the original owner of the copyright in the part that he has created;".
(http://www.chanrobles.com/legal7copyright.htm#.Vq9ZH9J9600)

Copying and Pasting without including quotation marks and the name of the original creator is plagiarism

"
-turning in someone else's work as your own
-copying words or ideas from someone else without giving credit
-failing to put a quotation in quotation marks
-giving incorrect information about the source of a quotation
-changing words but copying the sentence structure of a source without giving credit
-copying so many words or ideas from a source that it makes up the majority of your work, whether ---you give credit or not (see our section on "fair use" rules)".
These are some kinds of plagiarism, to avoid it, one must understand it. It is also better to be familiar with the legal statements the Law of Copyright holds. Especially for marketing people, and creative writing. Eventually, one phrase that is protected by the order using the Law of Copyright will encounter someone else saying the same phrase, therefore ending in a law suit.
(http://www.plagiarism.org/plagiarism-101/what-is-plagiarism/)

Plagiarism is not just something to describe one's way of copying someone else. It is a crime, and it is to be avoided. Even being forgetful in giving proper accreditation or mentioning the name of the photographer in a profile pic may be called plagiarism. Be careful and be respectful to creators, authors, and so forth.