In law, severability (sometimes known as salvatorius, from Latin) refers to a provision in a contract which states that if parts of the contract are held to be illegal or otherwise unenforceable, the remainder of the contract should still apply. Sometimes, severability clauses will state that some provisions to the contract are so essential to the contract's purpose that if they are illegal or unenforceable, the contract as a whole will be voided. However, in many legal jurisdictions, a severability clause will not be applied if it changes the fundamental nature of the contract, and that instead the contract will be void; thus, often this is not explicitly stated in the severability clause.
Severability clauses are also commonly found in legislation, where they state that if some provisions of the law, or certain applications of those provisions, are found to be unconstitutional, the remaining provisions, or the remaining applications of those provisions, will, nonetheless, continue in force as law. While this merely restates what is generally the law of most jurisdictions, it is nevertheless wise to include such language to make clear the parties' intent that only unimportant non-material provisions may be severed.
Many laws have clauses specifying clearly the exact opposite, in which only all parts of the law taken together can be enforced: This act is to be construed as a whole, and all parts of it are to be read and construed together. If any part of this act shall be adjudged by any court of competent jurisdiction to be invalid, the remainder of this act shall be invalidated. Nothing herein shall be construed to affect the parties' right to appeal the matter. (example New Hampshire statute)