A skill challenge is an encounter-style framework for non-combat encounters. It has turn-based play, but no grid or minis. D&D 4e formalized a structure for it, although I think they dropped it
In traditional 4e, the skill system is a simple closed, point-buy system. There is an enumerated list of non-combat abilities (skills), and you invest in a subset of them by choosing which skills
One of my priorities in how I GM is that I want the players to be active and engaged, not just act as my audience. So when I started planning out a new adventure with a heavy investigation