What does a 5% significance level mean?

Sure. In other words, a 5% significance level means a 95% confidence level, suggesting that you are 95% confident that there is a signal of an effect.

It sounds complicated. Could you please elaborate a bit more?

The probability of committing a Type I error is called the significance level and is often denoted by α. A significance level of 5% means there is a 5% possibility that you reject a null hypothesis when it is true.