The Latin word caveat means 'let her [or him] beware' (the third person singular of the present subjunctive of the verb cavēre 'to beware'). It is pronounced to echo either 'navvy-hat' (IPA: /'kævɪæt/) or 'wavy bat' IPA: /'keɪvɪæt/. In English, it is used as a noun, meaning 'a caution', 'a warning'. This can be legal: a contract, etc, may include a caveat, that if, for example, a secret agreement becomes publicly known, it will cease to have force. In academic circles, it is often a warning about the quality of evidence, data etc: a given pattern of activity may be said to be world-wide, with a caveat that no sources have been checked other than those in the English language.
The legal maxim caveat emptor means 'let the buyer beware' - in essence, that in a transaction, the buyer has responsibility to ensure that what is being bought is what is wanted. (Modern law has regulated some of the injustices apparent to some when they first hear this maxim.)
More fully, A Dictionary of Law says that caveat emptor is: "A common-law maxim warning a purchaser that he could not claim that his purchases were defective unless he protected himself by obtaining express guarantees from the vendor. The maxim has been modified by statute: under the Sale of Goods Act 1979 (a consolidating statute), contracts for the sale of goods have implied terms requiring the goods to correspond with their description and any sample and, if they are sold in the course of a business, to be of satisfactory quality and fit for any purpose made known to the seller. Each of these implied terms is a condition of the contract. However, in many commercial contracts the vendors attempt to exempt themselves from liability for breach of these terms. This will usually be valid unless the exclusion is unreasonable or unfair under the law relating to unfair contract terms. These statutory conditions do not apply to sales of land, to which the maxim caveat emptor still applies as far as the condition of the property is concerned. However, a term is normally implied that the vendor must convey a good title to the land, free from encumbrances that were not disclosed to the purchaser before the contract was made" (Law and Martin, 2009).