no dress code; free dress
Used in workplace, school, or event contexts to indicate that there is no prescribed attire; often seen in job postings or event descriptions.
This company has no dress code, so I commute in casual clothes.
The party invitation said 'dress code: free'.
私服 refers to one's own casual clothes, while 服装自由 describes the policy or state of having no dress code.
ドレスコード is a loanword for 'dress code'; 服装自由 is the native Japanese phrase for the absence of such a code.
Compound of 服装 (attire) and 自由 (freedom), literally 'clothing freedom'.