boston lettuce means: Butterhead lettuce is a variety with soft and pliable green leaves. They have a buttery flavor and texture, and they are lighter than bibb lettuce. (in Cooking Dictionary)
What else does boston lettuce mean?
This simple, soft-textured lettuce is part of the butterhead family. It has lots of small outer leaves and well-defined heads. This bland tenderness blends well with bitter leaves and super-crisp Romaine. (in Cooking Dictionary)