Upper- and lower-case alpha.
The Greek letter alpha (Α or ɑ) often appears in biochemistry. Sometimes it finds its way into discussions in Foldit.
The term "alpha helix" or "ɑ-helix" simply means helix. The "alpha" reflects the fact that the helix was the first type of secondary structure identified by X-ray crystallography.
The alpha carbon (sometimes "ɑ-carbon") is the key spot in protein backbone. It connects the amino group, the sidechain, and the carboxyl group. The alpha carbon is also the point of reference for the backbone angles known as phi and psi.
The capital alpha generally looks just like a capital Roman "A". Depending on the font, lower-case alpha may look just like lower-case "a", or it may show distinct "cow horns".