Why is theta used for?

Could you please elaborate on the usage of theta in its respective fields? I'm curious to understand why theta finds itself to be a valuable and pertinent tool in various applications. Could you explain the significance of theta and its specific purposes? I'm particularly interested in how it is employed in cryptography and finance, given its supposed role in these areas. Would you be able to provide examples or scenarios where theta is utilized effectively? Thank you for your time and explanation.