What's GENERIC32?

Thanks to trying to get a Javastation-1 running, I had occasion to run
into the oddity that is sparc64's GENERIC32.

This leads me to ask, just what is 32-bit here?  Not what's 32-bit
about the built executable - I can read documentation on the options
used - but what's different about those machines that calls for the
kernel to be built differently like this?

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