How to explain this "practice"

Hi Guggi,

Practice, in this case, is a noun, and it means the way (technique, method) you do something. See 1c, here.

A "best practice" means a technique that has shown to be particularly effective - the best of doing something.

Interviewing is used adjectivally - what type of practice? We're not talking about a way to cooking or drive or do computer programming. We're talking about how to interview someone. So we're talking about an interviewing practice.

Does that make sense now?

Excellent! I'm glad.

(By the way, one interviewing technique that's often effective is to NOT say anything after the person gives their answer, to see if anything good follows. People hate silence in a conversation, so if I finish speaking, and you don't start again, I'll probably say more. That's often when you'll get the good stuff.)