Hi Charles, Lambda is used to make a function: e.g., You could say def foo(x): return x - 3*x + 4*x**2 and then use foo in another situation where a function is required: print map(foo, [1,2,3,4,5]) [2, 12, 30, 56, 90] a shorter definition would be using lambda bar = lambda x : x - 3*x + 4*x**2 print map(bar, [1,2,3,4,5])