HHVM stands for "HipHop Virtual Machine" and is a virtual machine developed by Facebook. HHVM was originally developed to improve the performance of PHP applications, especially for large and complex applications running on the Facebook platform. Here are some key points about HHVM:

1. Aim and Purpose: HHVM was developed to execute PHP applications more efficiently. PHP is a widely used scripting language often used for web application development. HHVM aimed to boost the performance of PHP applications, especially for high-traffic websites like Facebook.

2. Just-In-Time (JIT) Compilation: HHVM uses Just-In-Time compilation to translate PHP code into machine-readable code. This enables faster execution of PHP code compared to traditional interpretation.

3. Hack Programming Language: In parallel with HHVM development, Facebook also created the Hack programming language. Hack is a statically typed extension of PHP that runs on HHVM. Hack adds additional features to PHP, such as static typing, and enhances error detection and prevention capabilities.

4. Facebook Application: HHVM was originally designed for running Facebook applications and was a crucial part of Facebook's infrastructure. It significantly improved the execution speed of PHP applications and reduced resource consumption.

5. Open Source: HHVM is an open-source project available to the public. Developers can download and use it to accelerate their own PHP or Hack applications.

However, it's worth noting that Facebook has decided not to actively use HHVM for running PHP applications anymore. Instead, Facebook has focused on using PHP 7 and later versions, which themselves brought significant performance improvements. Nonetheless, HHVM is still maintained as an open-source project and is used by other developers and organizations looking to benefit from its features.