Any material created by an outside source (person or company). Can include artwork, photographs, maps, logos, video footage, long excerpts of text. These works are usually protected by IP such as copyright or trademarks. This can also include any of your previous published works if you have signed a Copyright Transfer Agreement or an Exclusive Licence to Publish contract with a publisher.
There are a number of ways that you can copy third-party material within your work legally. You can: