Like all testing terms, the effective definition of alpha testing varies from site to site. Stricty, alpha testing is:
simulated or actual operational testing at an in-house site not otherwise involved with the software developers.
The wording of the definition is British in origin, but the concept is universal. The principle is that alpha testing should be the equivalent of beta testing, but performed onsite. Test execution should be independent of the coders themselves, and the results should form a baseline for determining whether problems found in beta are environmental.