The term is Paragraph breaks.
Line spacing ( applies to many lines within a paragraph block) is controlled by
line-height: 1.2 (is normal)
Make sure your conversion settings do not have remove blank lines.
(also, your device may need to use Publishers Stylesheet unless you hard encode blank lines
)
FWIW I gave up trying to get a 'perfect' conversion between formats. I hand edit my EPUB/AZW3 to add the FINAL polish
