For example, let's say you use a well-excepted data normalization method like z-normalization. To avoid clutter and help the flow of the paper, can you simply cite a source for z-normalization and move on, or will reviewers generally want to see everything formally defined in the paper itself? This assumes there is only one possible version of the technique being mentioned (if there were multiple, I would see why a full description would be needed).
It depends entirely on the specific journal you publish in, as well as the topic of your paper. The paper is meant to be read by other experts in your field: hence if something is well known, it doesn't need to be defined. For the average reader of your paper, will they already know what z-normalization is? If so, you don't need to define it.