Hmm. The very first words.....
"A semi-rigid main rotor is always a 2 bladed rotor system"
The head on the AS 350/355 is semi-rigid, if you read their training material. As the star is rigid drag-wise, it fits the definition. (To the original poster - that head supports three rotor blades.)
Given that it has elastomerics, I always thought that sem-articulated would have been a better term
Phil