What is "line spacing" / "leading"?

Name: Makoto Ueki
Email: makoto.ueki@gmail.com
Affiliation: JIS Working Group
Document: W2
Item Number: Success Criterion 1.4.8
Part of Item: 
Comment Type: general comment
Summary of Issue: What is "line spacing" / "leading"?
Comment (Including rationale for any proposed change):
We couldn't understand both "line spacing" and "leading". Could you explain both by using visual examples? There are multiple interpretation in Japan and both are confusing. For "line spacing" / "leading", We guess there would be differences among languages.

Proposed Change:
Need visual explanation on what "line spacing" is and what "leading" is. We'll be able to translate them if we see both.