What is the difference between standard error and standard deviation? std.error & std.deviation

What are the differences and connections between standard deviation and standard error? Both standard deviation and standard error are measures of variation, but there are differences as well as connections between them. Difference: ① Different concepts ； Standard deviation describes the degree of variation among observed values (individual values) ； The standard error describes the sampling error of the sample mean ； ②Different uses ； The standard deviation is used in combination with the mean to estimate the range of reference values, calculate the coefficient of variation, and compute the standard error, among other things. The standard error is used to estimate confidence intervals for parameters and to conduct hypothesis tests, etc. ③Their relationship with the sample size is different: when the sample size n is large enough, the standard deviation tends to stabilize ； The standard error decreases as n increases, and even approaches 0. Contact: Both standard deviation and standard error are measures of variation; when the sample size remains constant, the standard error is proportional to the standard deviation.