Difference between Greek and Latin letters in OLS Currently I am learning about the OLS method. In the literature I see different notations for the to be explained variable $y_i$. The different notations have to do with the letters used. In one notation Greek letters are used:
$y_i=\alpha+\beta x_i+\varepsilon_i$
In another notation Latin letters are used.
$y_i=a+b x_i+e_i$
In the literature I found the following:

When we analyse empirical data we do not know ‘true’ values of $\alpha$ and
$\beta$, but we can compute estimates a and b from the observed data.

So from this statement I understand that if we have a data set, we can only obtain $a$, $b$ which is an estimation for the true parameter. However, it is still not clear to me which notations are used in which context.
It is extremely helpful if somebody could point out the differences between the notations and in which context each notation is applicable.

A standard notation is to use Greek letters for the true parameter and to put hats on the Greek letters for their estimates, e.g., $\beta$ for the parameter and $\hat\beta$ for its estimate. Most any deviation from this would be somewhat nonstandard and require a definition by the author.
The more important issue is to understand the difference between the parameter being estimated and the estimation itself. The parameters are values that you posit exist, even if you cannot or will not observe them. Consequently, you collect data to make a guess (estimate) about the parameter, and much of statistics could be considered the science of making good guesses.
