Guts
Courage, Fortitude
noun
The kanji and the word are exactly the same. That means they share meanings as well.
胆 means guts, and just like the English word guts, it can also be used to mean courage or fortitude. However, 胆 is much more formal and advanced than its English equivalent, and it's almost always seen in the set phrase 胆が据わる (to have nerves of steel).
You learned this reading with the kanji, so you should be able to read it already!
お前はもう少し胆を練る必要がある。
You need to build up your courage.