Confidence means different things to different people. Generally, there are two types of confidence:

Epistemic confidence describes a person’s certainty about what’s true. When a meteorologist reports a 70% chance of rain, they are expressing epistemic confidence. 

Social confidence describes a person’s comfort with their social expression and role. When a person steps on a stage and speaks to 500 people, they are expressing social confidence.

If someone has ever told you that you need to be more confident, they’re usually talking about social confidence. They’re encouraging you to be more self-assured. They also want to make sure you feel comfortable being yourself around them.

You add value by being accurate and honest about your epistemic confidence—for example, saying “I don’t know,” when you don’t know, overselling them on something you don’t genuinely believe in, or distorting the past or present—and presenting yourself with high social confidence.

See also The Scout Mindset by Julia Galef, as well as this post by brit.