Plagiarism means using the words, work or ideas of another author without proper acknowledgement (intentionally or unintentionally).
Cutting and pasting from another author or work, including from the web, without attribution
Rewording another writer’s ideas or work, without acknowledgement
Representing the work of others as your own
If you are aware of what constitutes plagiarism and employ strategies to avoid it, you are much less likely to run into problems. A few strategies to help ensure that you will be able to properly acknowledge other authors include:
keeping careful track of the sources you read
when taking notes while reading, identifying clearly the sources of ideas you want to use in your writing