I use the OED definition, Mike, "halva", "halvah", "halvas", "halwa". = A sweetmeat made of sesame flour and honey -- i.e. based on tahini or sesame flour.
But there are many forms of the candy -- Wikipedia has I think one of the best discussions of the various forms on the Internet: The word halva is used to describe two distinctly different types of sweet, block shaped confections. One type of halva is based on semolina that is popular in India, Pakistan, and Persia. The other type is based on tahini, which is more popular in the east Mediterranean region.
I haven't tried to make any of the semolina based versions -- I love the tahini based type, either my own interpretation or the commercial types.
Candy, I've learned, is a vast field -- and it probably isn't so good for me -- an obsession with wine is enough.