# Changing plaintext for encryption in RSA [duplicate]

In the RSA crypto scheme, the message $x$ (plaintext), is encrypted to produce ciphertext ($y$), by computing $x^e \bmod n$. Of course, that means that $x$ has to be a numeric value for this to work, and I am assuming this is found by tables such as ASCII. But, what is this plaintext $x$? Is it a single character in the message, or larger parts of the plaintext that are encrypted together, as the examples I have seen have not really expanded on what $x$ really is, and have just given it a small numeric value for exampes, and I am interested to understand what $x$ is in practise.