If the HTML input does not contain any newlines around definition list tags:
import markdownify
md = markdownify.MarkdownConverter().convert
print(md("""
text<dl><dt>Term 1</dt><dd>Definition 1</dd><dt>Term 2</dt><dd>Definition 2</dd></dl>text
""".strip()))
then the Markdown output is also missing newlines:
text
Term 1
: Definition 1
Term 2
: Definition 2
text
New lines are required before/after <dl> tags and before <dt> tags as described here:
https://pandoc.org/MANUAL.html#definition-lists
https://michelf.ca/projects/php-markdown/extra/#def-list