An engineer that makes less impact than a staff engineer but more impact than a junior engineer.

An engineer who has been working some number of years, regardless of level of responsibility or skill, is a senior. If you've been working in the industry for 5 years and you're applying for junior positions then people are going to be really confused.

It's the minimum level of industry credibility.

I expect seniors to deliver on smaller to medium projects without external help. If someone can’t do that they’re not senior and i don’t care if they have 2 or 20 yoe

Senior eng these days is just someone who can deliver independently on a project of limited scope (within a single team purview)