Read this Monster Hunter World: Iceborne guide and walkthrough to find out what are breakable parts, including info & tips on how to identify monster parts to break.
What Are Breakable Parts?
Monster Weak Spots That Are Prone To Damage
Breakable parts in Monster Hunter World mean a monster's weak spots that are prone to damage. Each breakable part has a specific defense and damage needed to "break" them, making it important to choose which part to focus on with what weapon.
Hitting Broken Parts Can Increase Damage
When a Hunter breaks a monster part, that area is more prone to damage than before. Hitting these broken parts over and over again can help you bring the monster's HP down in order to defeat them.
How To Identify Breakable Parts
Check Color Of Damage Number
When you're hitting a breakable part or weak spot, the damage number will be "orange" but if you hit a normal spot that isn't weak, the damage number will be "white". This can vary depending on the type of weapon you use to hunt.
Check Ecological Research Monster Physiology
If you've gathered enough tracks and monster research, you can check the Physiology of each monster with the Ecological Research leader. This book will tell you the weak spots of each monster, including elemental weaknesses, & weapons to use for each part.