Hidden blocks (AKA 'hide and show' blocks, or 'dynamic' blocks) allow you to further personalise the content in your templates with dynamic data.
See also: Hide redeemed coupons in emails
In the visual editor, hover over a block and select on the cog icon, or click on the cog in the blocks list in the Edit template tab.
You can choose to display a particular block to a specific contact segment, lifecycle stage or the customer lifetime value (CLV) of the recipient:
For example, if you want to display different promotions depending on a customer’s lifecycle stage, you should add three copies of the same block and use the hidden block settings to select a different lifecycle stage or segment.
This means that if a recipient doesn’t belong to one segment/lifecycle stage they won’t see that block.