HSpice Manuals/Handbooks. What does Þ mean in the equations?
I believe you are referencing this 2005 version of the document (PDF page 151).  If you look at the same equation in this older 1998 version of a similar document (PDF page 6), this symbol is replaced by a multiplication dot, but without a space after it.  Both are snipped and shown below for direct comparison:

Therefore, I believe there's an encoding error in the PDF (as suggested in the comments), which is caused by the lack of a space after the dot.  So simply treat that symbol as a multiplication, or use the older document (if you can).