Operationalization of Variables

Just wanted to ask about the term ''operationalization' I kind of get the gist that it's about how you measure a certain variable beyond its definition.

Now, I'd like to ask say for example I want to operationalize 'gamified marketing' for my qualitative study. Should I look for qualitative studies ONLY as my reference or it doesn't matter as long as I find any excerpt that is relevant to how I want it to be operationalized?