Disclaimer means indemnification
In Practice It is a piece of text (this can be 2 lines, but sometimes also three pages) in which a person or a company does not accept liability for the service/service/product/website/etc.) On a forum the owner of the URL is not liable for the text that the users write, in an e-mail is the company where a person is not responsible for the text that a worker has written, etc.
If you don't feel like writing a disclaimer, check here for the use of a free disclaimer.