A Project Based Learning (PBL) environment is one in which students may work either independently or within groups as they explore creative (and often technology-based) solutions to open-ended problems of their choosing.
Many classrooms still rely on rote-memorization, paper-based assignments, and teacher-given lectures. In these classrooms, teachers may assign questions or challenges to students in order to guide learning.
Project Based Learning, on the other hand, places learning in the hands of students. Instead of choosing a guiding question and proposing certain choices or projects to demonstrate knowledge, teachers in PBL classrooms allow students to choose the direction of their learning. Their work and answers may veer from the predicted direction that the teacher envisioned!
"Project Based Learning" (from Edutopia)
"What Parents Need to Know About Project-Based Learning" (from Getting Smart)
"Why Project Based Learning?" (from the Buck Institute for Education)