21st century skills are simply defined as focusing on (a) critical thinking and problem solving; (b) communication; (c) collaboration; and (d) creativity and innovation, with technology-infused learning and assessment.
More complex definitions of 21st century learning include:
Empirically Based Knowledge and Skills; Higher-Order Cognitive, Metacognitive and Interpersonal Skills; and Global dispositions, perspectives, and attitudes; with Information literacy, Communication and Collaboration. College Board Global Education Framework (2011)
Digital-Age Literacy; Inventive Thinking; Interactive Communication; and High Productivity with Teaming, Collaboration, and Interpersonal skills; Interactive communication; and Effective use of real-world tools. EnGauge Framework from Metiri/NCREL (2003).
View this presentation on 21st Century Learning: