Playfulness is, first and foremost, a state of consciousness that concerns thought, speech, and action - the so-called "garments" of the soul. It begins at the level of thought and then naturally overflows into speech and action, like water finding expression in movement.
Observing our own playfulness and that of others (or the lack of it), we may suddenly realize that playfulness can be an excellent - and even cost-free ;-) - way to prepare our "vessels" for "light". Light is everywhere in abundance, but as long as our "vessels" are not ready - still filled with heaviness or "dust" - it cannot enter.
But what kind of state of consciousness is playfulness? Instead of defining it conceptually, which may already make us less playful), let us try to notice what characterizes this state so that it becomes more palpable to the mind and more livable in speech and action.
The first characteristic that comes to mind is lightness. We do not take life or ourselves too rigidly. We allow space. This does not mean we are not serious - on the contrary, we can be seriously playful, though that may sound contradictory at first.
We can feel this lightness in the presence of a playful person. The "air" around them is not dense or heavy but luminous and refreshing. Light attracts light, which is why playfulness is such a powerful way to prepare our "vessels" for "light".
The second characteristic is spontaneity. Even while writing these lines, we may feel as though we are simply allowing something to speak through us, like a scribe writing down a message. Spontaneity should not be confused with impulsiveness. The former comes from the soul and is supported by inner preparation (like improvisational dance), while the latter comes from the ego and reacts automatically.
The benefit of spontaneity is that it does not give the egoic mind time to intervene and block the "light". In moments of genuine spontaneity, egoic thought pauses, and something brighter shines through naturally. Again, light attracts light.
So, in short, playfulness consists of lightness and spontaneity. It is light-hearted spontaneity, or spontaneous lightness, according to your taste. ;-)
But even if we are convinced of the effectiveness of playfulness as a way to prepare our "vessels" for "light", we should not try to be playful. Straining to be playful has exactly the opposite effect. Instead, we simply relax, and allow playfulness to emerge on its own, lightly and spontaneously. ;-)