What a slug is
A slug is the part of a web address that names one particular page. In an address ending in /seo-services/local-seo/, the slug is local-seo: the section path sits in front of it, and the slug is the piece that identifies the page itself. Most content management systems generate one from the title when you first save a page and let you edit it afterwards.
The conventions are stable across platforms. Lower case, words separated by hyphens rather than underscores or spaces, no accented characters, no punctuation, and nothing that has to be percent-encoded. Anything else technically works, but it makes the address harder to share, harder to type and harder to read in a search result.
A slug is not a title and does not need to repeat one. Titles change; slugs should not, because the address is what other sites, emails and bookmarks point at.
Why slugs matter
The address is shown under or above the title in search results, so a readable slug tells a person what they are about to open before they click. It is also one of the few visible places where the subject of a page appears without any design around it — in a chat message, a support ticket, a printed leaflet.
Practically, slugs keep a site navigable for the people who maintain it. Consistent, descriptive slugs make redirects, analytics reports and internal linking straightforward. Reports full of addresses built from database identifiers take longer to read and invite mistakes.
Where slugs go wrong
Changing one without a redirect is the expensive mistake. The old address stops working, every link pointing at it breaks, and whatever authority those links carried is thrown away. If a slug must change, put a 301 redirect from the old address to the new one before the change goes live, and update your own internal links rather than relying on the redirect for ever.
Stuffing is the next fault: a slug that repeats the target phrase and adds the city, the year and the service again reads as spam and gets truncated in results anyway. Dates are a related trap — a slug containing a year commits you to either rewriting the address annually or leaving a page that looks stale.
Auto-generated slugs from long titles produce the third problem: addresses full of filler words that nobody can read or dictate over the phone.
Getting it right
Decide the slug when the page is created, keep it short, and make it describe the page rather than the whole site. A few meaningful words are usually enough; drop articles and connecting words. Use the same pattern across a section so that similar pages have predictable addresses.
Avoid encoding structure that will change. Product codes, campaign names and dates all age. If you publish in Nepali as well as English, be deliberate: transliterated slugs are readable in a browser but often become unreadable percent-encoded strings when pasted into messaging apps, which matters where most sharing happens on a phone. Above all, treat a published slug as a commitment — the cost of changing one is always higher than the cost of choosing it carefully.