Forging, Training
Noun and する verb
たんれん
発音が一晩で上手くなる人なんていません。発音を上達させるには、継続的かつ正しい鍛錬が必要です。
Nobody can get perfect pronunciation overnight. To improve your pronunciation you need continuous and proper training.
Forging and tempering of things is tempering and forging of things. When you do this to your body, to get ready for the big race, it's called training. (Though body tempering sounds way cooler, don't you think?)
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.