First, a question of common sense
This practice, as you will have understood, is not really a contemporary invention... It is rather the comeback of what was, a few decades ago, a question of pure common sense: when you break something, hey well, you fix it! An obvious fact that our modern societies have forgotten, in favor of new and ugly reflexes: broken object = thrown away object and bought new. A logic that has become untenable today, and which opens the way to a return to the good old pragmatism of the past, and to the care given to objects. As for the definition, the notion of reparability is not very mysterious. A repairable object is an object whose life span can be extended by replacing or repairing one or more parts.
It is opposed to another notion, much commented and pointed out for some time: programmed obsolescence, which describes a way of conceiving products with a limited lifespan, forcing consumers to buy them again regularly.
With reparability, on the other hand, we are following a virtuous and sober logic, that of the circular economy. Or how to get out of the linear pattern of produce > consume > throw away to come back to dynamics that are economical in resources and raw materials: produce > use > repair (or recycle) > reuse.