A tech stack is the set of technologies a product is built and run with: the programming languages, frameworks, database, hosting and main services.
Makers often share their stack publicly, and some directories list products by the tools they use.
For an early product, a familiar stack you can ship quickly with usually beats the newest option.
Why it matters for a launch
Listing your stack on launch pages helps developers find you and gives you a reason to be featured by the tools you use.