From reading as much as possible on the topic, I think what they are really looking for to satisfy this requirement is an elected or invited membership (like the national academy of science, or becoming an elected fellow of your society.
A lawyer here suggested that unless you have something like this, don't even attempt the category. Better to have a strong, concise case for other criteria than to dilute the officers time with memberships in societies that anyone in your field can join through a simple nomination process (ie most of the major societies that we all belong to, and don't really make you stand out from your colleagues).
