The paper introduces the concept of *squeezed spin states* (SSS) and discusses the principles for generating them. The authors propose two mechanisms, *one-axis twisting* and *two-axis countertwisting*, which reduce the standard quantum noise of coherent spin states. One-axis twisting can reduce the noise to \(\frac{1}{4}(S/3)^{1/3}\), while two-axis countertwisting can reduce it to \(\frac{1}{4}\). The paper also explores the implementation of these mechanisms in interferometers and two-level atoms. The authors clarify that a spin system is considered squeezed if the variance of one component normal to the mean spin vector is smaller than \(\frac{S}{2}\), and they emphasize the importance of quantum correlations in achieving this state. The paper concludes by discussing the potential applications of spin squeezing in interferometry and two-level atoms.The paper introduces the concept of *squeezed spin states* (SSS) and discusses the principles for generating them. The authors propose two mechanisms, *one-axis twisting* and *two-axis countertwisting*, which reduce the standard quantum noise of coherent spin states. One-axis twisting can reduce the noise to \(\frac{1}{4}(S/3)^{1/3}\), while two-axis countertwisting can reduce it to \(\frac{1}{4}\). The paper also explores the implementation of these mechanisms in interferometers and two-level atoms. The authors clarify that a spin system is considered squeezed if the variance of one component normal to the mean spin vector is smaller than \(\frac{S}{2}\), and they emphasize the importance of quantum correlations in achieving this state. The paper concludes by discussing the potential applications of spin squeezing in interferometry and two-level atoms.