The planned and systematic set of activities that ensure that software life cycle processes and products conform to requirements, standards, and procedures.
Sources:
CNSSI 4009-2022
from
NASA-STD 8739.8
The level of confidence that software is free from vulnerabilities, either intentionally designed into the software or accidentally inserted at any time during its life cycle, and that the software functions as intended by the purchaser or user.
Sources:
NISTIR 8074 Vol. 2
under Software Assurance