What's immediate superset? What's immediate superset?

Why is it called immediate?

They appear in the context of Apriori algorithm. Particularly the one enhanced with hashing.
Immediate often occurs simply to say that there are perhaps many supersets, e.g. when we have a tree like structure. There is also for example, the converse, an immediate subset.



Example

Set A has a superset B, and that superset has its own superset C. In this case, A must also be contained within C, but the set B lies within that realm and so is the immedaite superset of A.

Perhaps it is best visualised with a Venn diagram, where B is the immediate superset of A and equally the immediate subset of C:





There is some discussion here on Cross-Validated too, where the selected answer shows some further usage of the term (albeit in a slightly different context). Have a look at this source for some usage of the term, which leads you to my understanding.