Short answer
A URL slug is the part of a page address that names the page, such as blue-cotton-shirt in yourstore.in/products/blue-cotton-shirt. On Shopify it is called the handle. Keep it short, lowercase and hyphenated. The free slug generator on this site makes one from any name, and a whole list at once.
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What a slug is
The readable end of an address. It tells people and search engines what the page is about before they open it. In Shopify the product handle becomes the last part of the product address.
What makes a good one
Short, lowercase, words separated by hyphens, and about what the page is. Google recommends hyphens between words, not underscores. Drop small words if they make it long. Accents and symbols are removed.
Try it now: Slug Generator → · Shopify Redirect CSV Generator →
What to keep out
Colours and sizes in a product handle, when one product has several of them, because every variant shares the same address. Dates and years that will go out of date. Words repeated to chase a keyword.
Changing a handle on a live page
A new handle is a new address. The old one stops working unless you redirect it, and any links and rankings it earned are lost. Shopify offers a tick box to create the redirect when you change a handle, and it is worth ticking every time.
In bulk
Renaming or moving many pages needs a list of old and new addresses, and a redirect for every one. The redirect CSV generator on this site turns that list into a file Shopify can import.
Keep them stable
Choose a handle you will not need to change. A page that keeps one address for years collects links and trust that a rename throws away.