Bridge WAF
IP blacklist check: is this address on a list?
Queries public blocklists for an address and reports which of them name it. The answer is a fact rather than a judgement: a listing means some operator decided to add the address, on criteria that are theirs, at a time that may be long past.
What a listing actually means
Somebody put the address on a list, and that is all it means by itself.
Lists differ in what they collect. Some record addresses seen sending unsolicited mail, some record networks that allow it, some record ranges assigned to hosting rather than to households, and some record what was observed years ago and never revisited. Being named by one says something narrow; being named by several says the same thing several times if they share a source.
That is why the tool reports which lists name an address rather than producing a verdict. The lists disagree by design, and flattening them into a single answer would discard the only part that carries information.
When the address is yours
Two situations, and the useful first step differs.
Mail is being rejected. Listings that affect mail delivery usually publish a removal procedure, and the procedure is the route. What matters more is finding out why the listing happened, because a removal without a cause fixed is a removal that repeats.
A service is refusing your traffic. Here the listing may be incidental. Plenty of refusals come from reputation systems that never consulted a public list at all, and treating a listing you happen to have found as the cause can send you down a path that changes nothing.
When the address is somebody else's
This is the more common use, and the boundary is worth respecting.
A listing tells you what a list says about an address, not what the address is doing to you now. A visitor from a listed address may be perfectly ordinary, and an unlisted address may be the one causing your problem: lists lag reality in both directions. What the result is useful for is adding context to a pattern you already observed, not for deciding on its own who gets in. That decision belongs with the material on IP reputation, which is a different question with different inputs.
Questions
What does it mean if my IP is blacklisted?
That one or more list operators added it, on their own criteria and possibly some time ago. It does not by itself mean traffic will be refused: whether anything acts on a listing depends entirely on which systems consult that list and how much weight they give it.