expression
just kidding; I'm joking
A playful, casual expression used to retract a statement or indicate that one was joking. Often used in lighthearted conversation, similar to 'just kidding' in English. The ぴょん ending adds a cute or bouncy feel.
See also: ぴょん
明日テストがあるって言ったけど、うそぴょん！
I said there's a test tomorrow, but just kidding!
彼が怒ってるかと思ったけど、うそぴょんだった。
I thought he was angry, but he was just joking.
じょうだん means 'joke' in general. うそぴょん is more like a retraction or a lighthearted 'I was only joking' after saying something untrue.
A playful combination of うそ (lie) and the sentence-ending particle ぴょん, which adds a cute or bouncy nuance. The exact origin is uncertain, but it likely emerged from casual, youthful speech.