PEAR is a repository of PHP software code, designed to offer some functionality not built into PHP core
The PHP Extension and Application Repository, or PEAR, is a repository of PHP software code.
PEAR contains a repository of hundreds of PHP libraries, ranging from HTML form generation to an IMAP protocol implementation. Its use as a package manager (for both PEAR and PECL) has been deprecated (it throws numerous warnings if you run it under PHP 5.4 or later). PEAR libraries, being normal PHP files, can be downloaded directly and included like any other PHP file. If you need a package manager for PEAR, you can use PEAR2 Pyrus, which is written in phar
Stig S. Bakken founded the PEAR project in 1999 to promote the re-use of code that performs common functions. The project seeks to provide a structured library of code, maintain a system for distributing code and for managing code packages, and promote a standard coding style. Though community-driven, the PEAR project has a PEAR Group which serves as the governing body and takes care of administrative tasks. Each PEAR code package comprises an independent project under the PEAR umbrella. It has its own development team, version-control and documentation.
See http://pear.php.net/ for more information.