Welsh rabbit is a snack dish, also known as toasted cheese. It is one of the simple pleasures of British cuisine. It is made by grating cheese, blending it with beer or a little milk and butter, seasoning, and spreading the mixture onto hot toast; the whole is then grilled - in the British fashion, i.e. heated briskly from above. (called broiling in North America)
'Welsh rabbit' is a disguised 'Welsh joke.' In a traditional society where even a half-grown stripling could snare a rabbit for the pot, a Welshman was considered (by the English of course), so hopelessly feckless that cheese melted with beer would have to substitute. Victorian and later Recipe books often refer to this dish as "Welsh rarebit". This is a silly euphemism, and all dictionaries agree that it derives from an erroneous folk etymology.