It could be as straightforward as some Q&A which would enable the teacher to evaluate if the objectives had been met, and what the students had actually taken in during the lesson. It could involve asking them some questions which might make them think further about the lesson topic. It could be a short quiz. It could be student self or peer evaluation task. It rounds off the lesson and hopefully consolidates some of the learning. In art, it might be something like gathering all the work together and discussing which pieces worked really well as a whole group or even smaller groups of four of so - getting them to point out what they think really worked and why.