What is a stx in USD?

Could you possibly explain to me what exactly does the abbreviation "STX" represent in terms of the US Dollar (USD)? I've been hearing a lot about it in the context of cryptocurrency and finance, but I'm still not entirely clear on its definition or value in relation to USD. Could you also elaborate on how the value of STX might fluctuate in comparison to USD? I'm quite curious to understand its role in the broader financial ecosystem. Thank you in advance for clarifying this matter for me.