The unfortunate collision of the word "kernel" as in "kernel density estimate" and the separate use as in "reproducing kernel Hilbert space" is making the kernel tag kind of confusing.
The tag wiki summary has as its second sentence
DO NOT USE this tag for [kernel-trick] which is reserved for kernel methods in machine learning.
(as was @gung's suggestion here). But the first page of the "active" page for the tag currently shows only 4/15 questions about kernel smoothing and the remaining 11 about RKHS kernel functions. So it seems that the outcome of this discussion from last fall wasn't enough to clean up the tag.
The current space of kernel-related tags seems to be:
- kernel, supposed to be for KDE-style kernel functions but in practice a mix of both (264 questions)
- kernel-trick, for RKHS-style kernel functions and related issues (85 questions)
- kernel-density-estimate, for KDE in general (78 questions)
- kernel-regression, 5 questions of which 4 are about Nadaraya-Watson kernel regression (analogous to KDE) and 1 is about RKHS kernels
- renaming kernel to kernel-smoothing
- completely removing kernel and sorting it into kernel-density-estimate and kernel-regression as appropriate.
In either case, people who should be using kernel-trick will then hopefully pause after typing in "kernel", see two options, and hopefully read the tag summaries and pick the correct one.
I'm happy to do that sorting (a few at a time during low-traffic times).