The opposite of abstract thinking. Only thinking about specific, real things that actually exist and you have to deal with, rather than constantly thinking in hypotheticals etc. It involves confronting the definite, physical, "embodied" aspects of problematic experiences, rather than thinking too abstractly about the causes and effects.

From the paper:

"In CNT, the training exercises involved patients’ identifying a recent mildly to moderately upsetting difficulty and working through standardized steps to facilitate concrete thinking: (i) using mental imagery to focus on sensory details during the difficult event, noticing what is specific about the event and the context in which it occurs; (ii) noticing the process and sequence by which the difficult event unfolds (‘How did it happen?’), including warning signs and actions that may have influenced its outcome; (iii) focusing on how to move forward by specifying the particular steps and behaviours to do next (Watkins, 2009; Watkins et al. 2009)."