Definition from Nolo’s Plain-English Law Dictionary

1) To refuse or give away a claim or a right to something. For example, if your aunt leaves you a white elephant in her will and you don't want it, you can refuse the gift by disclaiming your ownership rights.
2) To deny responsibility for a claim or act. For example, a merchant that sells goods secondhand may disclaim responsibility for a products defects by selling it as is.

Definition provided by Nolo’s Plain-English Law Dictionary.