I am a total newbie (and don't apologize for it!) What does the operator "lambda" do? What does it mean?

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Short answer : lambda is used to create short and anonymous Python functions. For example, instead of writing:

sage: def inc(n):
....:     return n+1

You can write:

 sage: inc = lambda x : x+1

but lambda x : x+1 can be used directly in your code, without needing to name it inc, while the def construction require to give a name and use return

Longer answer : http://www.sagemath.org/doc/thematic_...

To answer an implicit question of why you might use them, sometimes there are functions you want to do something with in Sage that are not symbolic - see e.g. this documentation or here.