Focus on Form
Michael H. Long is the originator of this term.
See his online article, Focus on Form in Task Based Language Teaching, from which comes:
... during an otherwise meaning-focused lesson, and using a variety of pedagogic procedures, learners' attention is briefly shifted to linguistic code features, in context, when students experience problems as they work on communicative tasks, i.e., in a sequence determined by their own internal syllabuses, current processing capacity, and learnability constraints. This is what I call focus on form.
Other references
Incremental Focus on Form in Second Language Learning by Shawn Loewen, University of Auckland.