The human-readable name you buy and own (tiffinbox.com), and the full address of a specific page on it.
Why it exists
People cannot remember or trust a raw string of numbers, and you need a name that is unambiguously yours and cannot be taken while you pay for it. A domain exists as that owned, human-readable name, and the URL extends it into the exact address of one page inside your product. Because the name is a rented asset with a renewal date, letting it lapse has taken real companies fully offline, and how you structure the addresses under it affects both sharing and search ranking.
How it actually works
A domain is the name people type and remember. You buy it from a registrar and it is yours to point wherever you like. A URL is the complete address, including the domain plus the path to a specific page: tiffinbox.com/menu.
The domain is the brand and the front door. Everything else in the address describes where inside your product a link goes.
A senior PM walks you through it
A junior PM, stuck
Marketing wants the Eid campaign to live on its own address, and I am being asked to choose between a subpath, a subdomain, and a brand-new domain. I do not actually know what each part of a web address is, so I cannot say which choice is cheap and which one commits us to something. I do not want to pick the expensive option by accident.
A URL looks like one blob, but it is a stack of parts and each one is a different decision owned by a different team. Once you can name the parts, the subpath-versus-subdomain-versus-new-domain question answers itself, because each option is just changing a different piece of this same address. Here is the exact URL marketing sketched, split one piece per line, so we can point at what each option actually touches.
https://store.tiffinbox.com/menu/kacchi-special?src=eid-campaign, one piece per line
The full address, split part by part
1https://
2store.
3tiffinbox
4.com
5/menu/kacchi-special
6?src=eid-campaign
Click a step to see the lines it points at.
Mistakes I've seen
Buying a new domain for a short campaign. It commits you to a renewal forever, needs its own certificate, and starts search ranking from zero, all of which a subpath under tiffinbox.com gets for free.
Assuming a subdomain is just the same site with a prefix. store.tiffinbox.com is a separate host, so it needs its own certificate and a login set on the main domain does not carry over to it.
Forgetting the domain has a renewal date. The name is rented, not owned outright, and a missed renewal has taken real companies fully offline; that is a calendar and billing problem, not an engineering one.
Treating the query string as part of the page's address. ?src=eid-campaign is attribution metadata the page reads; the identical page loads whether or not it is there.
Reply with: "Let's run the Eid campaign on a subpath, tiffinbox.com/eid, not a new domain or a subdomain. The subpath keeps one certificate, inherits our existing search ranking, and needs no registrar work, and the src query tag still gives us clean attribution." You split a URL into scheme, subdomain, domain, TLD, path, and query, and matched each option to the part it actually changes. That is the skill.
Where a PM meets this
Domains are owned, renewed, and can expire. A lapsed domain renewal has taken real companies offline.
Clean, readable URLs matter for sharing and for search ranking; PMs weigh in on how they are structured.
Hear it in a meeting
"Let's keep the campaign on a subpath, not a whole new domain."