The phrase "same axle" refers to two or more things that are connected or placed on the same rod or shaft, making them move together or function as a unit. Full definition
Its normally a good idea to replace both springs on the same axle together, as just replacing one may result in a different ride height or stiffness on one corner of the car afterwards. (mechanics.stackexchange.com)
It is always recommended to replace suspecsion and braking components on both sides of the same axle at the same time, wherever possible. (mechanics.stackexchange.com)
Locking differentials force driven wheels on the same axle to rotate at the same speed, regardless of traction, or lack thereof. (automobilemag.com)