A PLN or Personal Learning Network is a system that teachers can use to continue learning through online resources and connections with other educators. The document lists several potential online tools that can be used to build a PLN, including social networking sites like Facebook, bookmarking sites like Delicious and Diigo, blogging platforms like Ning, and microblogging on Twitter. It encourages teachers to explore and select from these options to develop their own personalized professional learning network.