From Longman Dictionary of Contemporary English chosen field/career/profession etc the job or activity you have decided to do He was very successful in his chosen career as a barrister. → chosen

Chosen automatically sets the default field text ("Choose a country...") by reading the select element's data-placeholder value. If no data-placeholder value is present, it will default to "Select an Option" or "Select Some Options" depending on whether the select is single or multiple.