In law, severability (sometimes known as salvatorius, from Latin) refers to a provision in a contract or piece of legislation which states that if some of the terms are held to be illegal or otherwise unenforceable, the remainder should still apply.
[1] A broad example would be one like this: If any one or more section, subsection, sentence, clause, phrase, word, provision or application of this Ordinance shall for any person or circumstance be held to be illegal, invalid, unenforceable, and/or unconstitutional, such decision shall not affect the validity of any other section, subsection, sentence, clause, phrase, word, provision or application of this Ordinance which is operable without the offending section, subsection, sentence, clause, phrase, word, provision or application shall remain effective notwithstanding such illegal, invalid, unenforceable, and/or unconstitutional section, subsection, sentence, clause, phrase, word, provision or application, and every section, subsection, sentence, clause, phrase, word, provision or application of this Ordinance are declared severable.
(example New Hampshire statute)[2] A more extreme variant is a clause specifying all parties should undo all the gains they earned due to that law/contract if any provision is adjudged to be invalid.
In court systems within constitutional law countries, judges may employ a severability doctrine when they deem one or more clauses of a passed statute as unconstitutional.
Supreme Court Justice Brett Kavanaugh wrote in his lead opinion in Barr v. American Assn.