As a heuristic, I would guess that it is anything that is enjoyable, and/or valuable to you in itself, and that you would do for free.
This could be anything from the singing and wordplay games you and your family/community engage in while you tend to your forest garden, to playing a language-learning RPG.
A lot of the things that come naturally when you aren't alienated from your labour could be considered productive play, I think.
An_Old_Big_Tree wrote
As a heuristic, I would guess that it is anything that is enjoyable, and/or valuable to you in itself, and that you would do for free.
This could be anything from the singing and wordplay games you and your family/community engage in while you tend to your forest garden, to playing a language-learning RPG.
A lot of the things that come naturally when you aren't alienated from your labour could be considered productive play, I think.