I am looking for a word or expression for things that are meant to be stacked. Though there are several generic words for things, I could not come up with a good term for this purpose.
For example, "block" is too generic in the sense that it could be laid out in arbitrary fashion though by itself I could define it in advance just for the purpose of the context of stack. "module", "entity" and others also lack the right amount of specificity.
I am describing a logical unit of content which can include this thing(s) inside, which cannot stand side by side but only vertically. As it will be widely used in user documentation and so, I hope to come up with a better word than "module", "block", "box", "object" and so on.