Shulman says pedagogy and content knowledge (PCK) must be considered together.
Hughes add technology to form TPCK (Technological Pedagogical Content Knowledge
Mishra and Koehler articulate the interdependence of content, pedagogy and technology knowledge
TPCK becomes TPACK as Thompson and Mishra say it better represents the interdependence of the three domains and represents the "Total PACKage" of teacher knowledge required for technology integration.
TPACK becomes Tech-PACK as Roblyer and Doering emphasize the critical contribution of technology to teaching.
(Source: Roblyer & Doering (2013))