[TommiTheTaco]

Zhuy. Here. This should clear it up for you.

If a boxer is doing conditioning, that means he/she is training their body to face the extreme requirements of the fight(withstanding punches, leaning, bobbing and weaving, throwing their own array of punches, moving around the ring, getting up from a knock-down).

The definition of endurance:

en⋅dur⋅ance
   
–noun
1. the fact or power of enduring or bearing pain, hardships, etc.
2. the ability or strength to continue or last, esp. despite fatigue, stress, or other adverse conditions; stamina: He has amazing physical endurance.
3. lasting quality; duration: His friendships have little endurance.