1. The act of adopting, or state of being adopted; voluntary acceptance of a child of other parents to be the same as one’s own child.  
2. Admission to a more intimate relation; 
3. The choosing and making that to be one’s own which originally was not so; acceptance; as, the adoption of opinions.
4. (computing) Transfer between an old system to another (usually better) system

Adoption is another word that can mean different things based on what an individual cares about for themselves or their role. As part of a process improvement or digital transformation it usually is a measurement of how much the new system is being used in production.