[gipp]

It is an extremely common acronym.

[vidarh]

It's an extremely common acronym in a small niche. So while you're right, sort of, it's still worth clarifying when posted to a more general site.

[lloydde]

It’s not a small niche. Search any job board and ETL will show up in a large presentage of job posts and resumes related to software QA and data validations.

[spc476]

HTML does have the <ABBR> tag. How hard is it to do?

    <abbr title="Extract, Transform, Load">ETL</abbr>

Even once?

[lloydde]

I was not disagreeing with the recommendation. It’s almost always a good idea to spell out an acronym/initialization on first use.

[_jal]

It is the kind of acronym that is known by anyone who needs it, modulo those two random people somewhere in the world who just discovered today that they need it but haven't googled the problem yet.

Admittedly, it is also the sort of acronym that, when you don't know it, is really annoying in a headline.