What are Lambda productions

I'm taking a computational structures course and we just started going over context free grammars. I was confused when I started seeing lambda productions. What are they? Can't seem to find an answer anywhere.

$\lambda$ (lambda) is sometimes used to denote the empty string. Thus, a "lambda production" is a production like $A \to \lambda$, i.e., a production that allows a non-terminal to generate the empty string.
Other sources will use $\epsilon$ (epsilon) to denote the empty string. They might refer to them as epsilon productions. They're the same thing. It's just a difference in notation.
• @user406955 Not quite, since any production resulting in a terminal string (e.g., $A\to b$) is a leaf. $\lambda/\varepsilon$-productions are productions that generate nothing at all. – David Richerby May 6 '17 at 11:04