What are Lambda productions
$\lambda$ (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.