The term "theological liberalism" is thrown around a lot.
When push comes to shove though, it still boils down to Richard Niebuhr's summation of what theological liberalism truly is: "A God without wrath brought men without sin into a kingdom without judgment through the ministrations of a Christ without a cross" (Kingdom of God in America, 193).
Liberal/progressive Christianity is more than that but it is no less than that, and it will always come down to it. Niebuhr's words 89 years ago are just as applicable in 1937 as they are today.