Reconstitution
Reconstitution is the step of adding a sterile liquid to a freeze-dried powder so that it becomes a solution again.
The word names one action and nothing more. It is not a technique or a protocol, and the word itself carries no information about how much liquid, which liquid, or whether it should be done at all.
Adding liquid never changes how much compound is present. It changes the concentration, and therefore how many marks on a syringe a given amount will occupy.
For example
A 10 mg vial with 2 mL of liquid added holds 10 mg dissolved in 2 mL — a concentration of 5 mg/mL. The vial still contains 10 mg.
What it is not
Reconstitution is not dilution in the loose sense of making something weaker or safer. It is not a purification step, and it does not make anything sterile that was not sterile already.
Where this comes up: reconstitution, reverse