Beta definition

Identifying a molecular position in an organic chemical compound.
Designates the second in an order of precedence.
Preliminary; prerelease. Refers to an incomplete version of a product released for initial testing.

The name of the second letter of the Greek alphabet (Β, β), preceded by alpha (Α, α) and followed by gamma, (Γ, γ). In modern Greek it represents the voiced labiodental fricative sound of v found in the English words have and vase.
Used in marking scheme: α, β, γ or α+, α, α-, β etc.
Average sensitivity of a security's price to overall securities market prices.
The phase of development after alpha testing and before launch, in which software, while not complete, has been released to potential users for testing.
A computer program in such phase; a preliminary version.
Information about a route which may aid someone in climbing it.
A beta particle or beta ray.
A beta fish, of the genus Betta.

To preliminarily release computer software for initial testing prior to final release.
To proofread a text, especially fan fiction.
- 1999, sqira a., in alt.tv.x-files.creative http://groups.google.com/group/alt.tv.x-files.creative/msg/29d32d27e61755f2?dmode=source
  
  My thanks to Heather; who read it and betaed it. Thank you.
- 2000, Elizabeth Durack, quoted in Angelina I. Karpovich, “The Audience as Editor: The Role of Beta Readers in Online Fan Fiction Communities” (essay), in Karen Hellekson and Kristina Busse (editors), Fan Fiction and Fan Communities in the Age of the Internet, McFarland (2006), ISBN 9780786426409, page 180,
  
  Beta’ing is time-consuming, so asking a lot of people to give you a detailed analysis isn’t the most polite thing to do.
- 2002, Jane Davitt, in alt.tv.buffy-v-slayer.creative http://groups.google.com/group/alt.tv.buffy-v-slayer.creative/msg/9301606b391212c0?dmode=source
  
  The next part is written and beta'd (thanks, Jen!), ready to go but <shuffles feet> I haven't even started what should be the final part yet.
- 2002, Karmen Ghia, in alt.startrek.creative.erotica.moderated http://groups.google.com/group/alt.startrek.creative.erotica.moderated/msg/8405f53e8acbb0c1?dmode=source
  
  I had the honor of betaing this story and as I was doing the first read through I had the odd, but lovely, experience when a story suspends the reader in its own rhythm and flow, its own reality.