Ensembles are a great concept. Basically, they are a group of top performers that build something fantastic together. The guys over at I Hate People have a great post that explains the ensemble.
For the entrepreneur, the ensemble is your core team. These are the people you bring together to get your company off the ground. Another important aspect of this is the realization that adding more bodies to a team will not make the project go faster. They have to be the right people, at the right time, with the right skills and have the right attitude for the ensemble.