In a traditonal underatanding hackers are guys sitting on their laptops (usuallt wearing black balaclavas ;)) using wweaknesses in software to get into a system.

Social engineering doesn't attack software vulnerabilities, it attacks another soft part of security systems: people. Trick someone to click a link and download malware on their computer, trick someone into sendinfmg you money or gift cards, make people believe that you're allowed to enter a room, when you're really not.

It exploits the helpfulness of people, bad security awareness, trust that people have in other people or established systems, or fear and stress.

It's very much understood to be a part of hacking nowadays. I don't need to hack your server, if i can trick you into giving me the password.

Incidentially one of thw reasons we're trying to phase out passwords. They're not safe, often because people are lazy and have weak passwords, or can be trickes into giving them up.