Glossary
What is a membership tier?
A membership tier is a group that decides what the people in it can reach. Every account sits on one: full and associate, standard and premium, whatever yours are called. Content is published to tiers rather than to individuals, so moving somebody up changes what they can open.
Still deciding
See the terms as features
The glossary explains the vocabulary. The features page shows what each of these looks like in a portal you run yourself, and the pricing page shows what it costs.