In the realm of filtering data or information, the term "subfilter" refers to a secondary filter applied to a refined subset of data. However, if you're seeking alternate words to convey a similar meaning, there are several synonyms available. For instance, "secondary filter" can be used to describe an additional level of filtration. Another option is "narrowing filter", which denotes the process of narrowing down a selection through a refined filter. "Refined filter" also works to convey the idea of filtering data to a more precise level. Lastly, "subset filter" implies the act of filtering a subset of data rather than the entire pool. These synonyms offer alternative ways to describe the concept of a "subfilter."