/ˈɑpʃənl ˈstændərd/ – Phrase
Definition: chuẩn mực tùy ý chọn, chuẩn mực không bắt buộc.
A more thorough explanation: An “optional standard” refers to a standard that is not mandatory but may be adopted or followed at the discretion of the parties involved. It is a guideline or specification that is not required by law or regulation, but may be used as a reference or benchmark for best practices or quality control.
Example: Participation in the training program is voluntary, but completion of the optional standard assessment is recommended for professional development.