In its most basic form, plagiarism is the act of presenting stolen creative works as original work. It does not matter if the act was accidental or intentional and covers both copyrighted works and works in the public domain. While plagiarism and copyright are related it is possible to infringe upon copyright and not commit plagiarism. The best way to prevent plagiarism is to correctly attribute your sources and do your own work.
Attribution, or Acknowledgment, is giving credit to the original content creator and creating a resource for your audience to discover your sources. Attribution does not absolve you of copyright infringement, which grants the original content creator exclusive rights, but it does prevent plagiarism. Attribution is always found on or directly next to the sourced item and usually also included in a works cited or bibliography page.
Infringment is the act of replicating, claiming, or using materials protected by intellectual property rights without the permissions of the rights holder.
Is failing to meet or breaking the terms of a contract licensing or otherwise concerning rights to intellectual property. In many cases this happens with trade secrets and non-disclosure agreements, but can occure any time intellectual property rights are shared with a person or company beyond the content creator.
Counterfeit items are those that are intended to be mistaken for an item that carries a patent or protected industrial design. Sometimes counterfeit items are called forgeries and usually refer to physical items but can also include digitial materials such as software. Piracy is duplicating exact copies of creative intellectual property (usually copyrighted, trademarked, or patented works) for distribution.