"Residential IP" gets used two ways: as a plain technical classification (an address registered to a home internet subscriber) and as a marketing term for proxy and VPN services selling access to exactly those addresses. Understanding the technical meaning first makes the marketing use easier to evaluate.
What makes an address residential
An address is classified as residential based on how it's registered and allocated — typically to an ISP's consumer broadband service, as opposed to a business line, a datacenter, or a mobile carrier network. IP intelligence providers determine this from registry records and observed usage patterns, not from anything about the specific person using the connection at a given moment.
Why residential classification matters to services
Many websites and services treat residential-classified traffic as lower risk by default, on the theory that residential addresses are harder to acquire in bulk than datacenter or proxy ranges, making large-scale automated abuse less likely (though certainly not impossible) from that network category.
Why residential doesn't mean trustworthy
This is the important nuance: residential classification is a fact about network ownership, not a guarantee about current behavior. A residential address can be dynamically reassigned to a new household whose previous occupant caused abuse, or can be temporarily compromised by malware without the classification changing at all. See Residential IP Reputation for more on why "residential" and "clean" aren't the same thing.
The "residential proxy" industry
A separate but related topic: some commercial services specifically sell access to IP addresses that carry residential classification, routing traffic through real consumer connections (sometimes with the consumer's knowledge and consent, sometimes not). This is worth understanding as its own topic — see Residential Proxies.
FAQ
Is my home internet connection automatically classified as residential?
In almost all cases yes, assuming it's a standard consumer broadband, cable or fiber connection from your ISP rather than a business-tier line.