Gearman is an open source job server that allows distributing asynchronous jobs across multiple servers. It provides a way to queue tasks and process them in the background with workers. The speaker discusses how Gearman can help build scalable PHP applications by distributing workload across servers. He demonstrates how to create PHP clients to submit jobs and PHP workers to process jobs. Managing many worker processes poses challenges which his company addressed in a Gearman Agent Manager tool for centralized monitoring and control of Gearman workers.