A beta launch opens an unfinished product to outside users, on the understanding that it has rough edges and that their feedback will shape it.
A closed beta is by invitation; an open or public beta lets anyone in. Either way the label sets expectations: people forgive bugs in a beta that they would not forgive in a finished product.
A beta is only useful if you ask for feedback and act on it. Give testers one obvious way to reach you and answer quickly.
Why it matters for a launch
Beta users are the easiest first users to get, because being early is itself the appeal. The ones who stay become your first customers and your first word of mouth.
Read more: How to get your first users