"And/or" means any combination of two options; one, the other (either), or both.
In law, it is synonynmous with "or" which is taken to mean the same thing, and which is a preferred term for the concept of "either or both", which and/or attempts to convey.
"And/or" is considered poor legal drafting and has been much criticized by the courts.
It is to the law as the square root of 2 is to mathematicians, an "irrational" word.
It has been called a "pestilent" and a "montrous linguistic abomination".
"'And/or', that befuddling, nameless thing. That Janus-faced verbal monstrosity, neither word nor phrase, the child of a brain of some one too lazy or too dull to express his precise meaning, or too dull to know what he did mean."
Brown v Guaranty Estates Corp. 239 NC 295 (1954)