Extra Trees (Extremely Randomized Trees) the ensemble learning algorithms. It constructs the set of decision trees. During tree construction the decision rule is randomly selected. This algorithm is very similar to Random Forest except random selection of split values.
P. Geurts, D. Ernst., and L. Wehenkel, Extremely randomized trees, Machine Learning, vol.63, pp.3-42, 2006
License for Scikit-Learn implementation of Extra Trees: New BSD License