From Longman Dictionary of Contemporary Englishwalk-in business/clinic/centre etcwalk-in business/clinic/centre etca business, doctor’s office etc that you can use or go to without having previously arranged a time to do this → walk-in
Examples from the Corpus
walk-in business/clinic/centre etc• The walk-in centre is the result of two years' struggle by an international group of scientists to realise an ideal. 