What does "犊不畏虎" mean? I would like to know what the following Chinese expression means.

犊不畏虎。

I know what it literally means by deciphering the meanings of individual Chinese characters, that a calf is not afraid of a tiger, but what does it "imply" exactly?

How would this expression be used?

Is the expression above used frequently in modern times, or is it an outdated expression?

Are there other equivalent expressions in Chinese?
It is actually written as "初生牛犊不怕虎”，it is sometimes used to describe a person not afraid of an strong enemy because he/she is a novice or beginner. Not very often, but is is commonly used.