URL

The address of a resource: scheme, host, path, query and fragment.

Backend Engineer · Junior · core Frontend Engineer · Junior · core Data Engineer · Junior Data Analyst · Junior

Also known as: Uniform Resource Locator, web address, link, URI

A URL is the address of a resource on the internet. Every part has a job:

https://user@shop.example.com:8443/products/42?color=red&page=2#reviews
└─┬─┘   └─┬─┘ └──────┬───────┘└─┬─┘└────┬────┘└──────┬───────┘└──┬───┘
scheme  user   host (domain)  port  path       query         fragment

Part	Meaning
Scheme	The protocol: `https`, `http`, `ftp`…
Host	The server’s domain name or IP address
Port	Which service on that host (omitted when it’s the default: 80 for HTTP, 443 for HTTPS)
Path	Which resource: `/products/42`
Query	Extra parameters after `?`, as `key=value` pairs joined by `&`
Fragment	A spot within the page, after `#`. The browser doesn’t send it to the server

Practical points

Special characters must be encoded (a b → a%20b). See URL encoding.
Absolute vs relative. https://example.com/a is complete; /a is relative to the current host; ../a relative to the current path.
Don’t build or parse URLs with string tricks. Use the language’s URL tools:

const url = new URL("https://example.com/search");
url.searchParams.set("q", "red kettle");
url.toString();      // "https://example.com/search?q=red+kettle"

from urllib.parse import urlparse, urlencode
urlparse("https://example.com/a?x=1").netloc      # 'example.com'

Don’t put secrets in URLs. They’re logged, saved in history and sent in referrer headers.
Two URLs with different origins are treated separately by the browser’s security rules.

“URI” is the broader term (it includes names without a location); in everyday use, people say URL and mean the same thing.