What exactly is an ellipsis?

Hello there,

I please need help answering the following question concerning the grammatical process called "ellipsis" in linguistics:

Is an ellipsis an omission of words in a sentence in general, or is it rather such kind of an omission but

restricted to specific, well-defined cases?

I have already figured out that what is called an "ellipsis" is a deletion of whole words from a sentence,

in opposite to a so-called "elision", which is the deletion of only sounds from words in themselves and not of the whole words.

In addition, the difference between the ellipsis applied deliberately as a stylistic device and the ellipsis as a linguistic process, i.e. the omission of words in general, has to be considered.

For this post, I am only talking about the ellipsis as a linguistic process and not about the stylistic device.

I now just can´t understand whether such kind of an ellipsis only can comprise certain well-defined cases of omission of words, or whether, in contrast, the general behavior of leaving out words in speech or writing can already be called an "ellipsis".

Thanks in advance for your answers.