# What is the difference between "Shot-Noise-Limit" and "Standard Quantum Limit"?

It seems that in a lot of papers in the field of quantum metrology, there are two terms Shot-Noise-Limit and Standard Quantum Limit which are frequently referred to. What's the difference between them, because it seems they all refer to the limit $$\Delta \theta\ge\frac{1}{\sqrt{N}}$$.

...the average of a large number $$n$$ of independent measurements (each having standard deviation $$\Delta \sigma$$) will converge to a Gaussian distribution with standard deviation $$\Delta \sigma / \sqrt{n}$$, so that the error on average scales with $$n^{-1/2}$$.
Metrology and optics both leverage the CLT. In quantum metrology, the statistical scaling of errors with $$n^{-1/2}$$ is referred to as the 'standard quantum limit'. In this more theoretical context, the exact definition of $$n$$ is left ambiguous. In quantum (and classical) optics, the precision limit in optical phase sensing (i.e. the minimum uncertainty) is the shot-noise limit. In this more experimental context, $$n$$ is given an exact definition, e.g. the number of photons.