OTU definition in MEGAN vs QIIME

I am new to this forum, I have a very basic question and I apologize if it was asked before. How do you define OTU in MEGAN, are sequences clustered under the same node or leaf considered a single OTU, or every single sequence read making up the node is considered a distinct OTU?

MEGAN doesn’t do OTU picking or clustering. Rather, It bins reads to known reference sequences (so in a sense, the reference sequences are the OTUs)