thick-bordered box; thick-bordered table
Refers to a box or table with a thick border, commonly seen in forms, documents, or layouts to emphasize a section.
申込書の太枠の中に必要事項を記入してください。
Please fill in the required information inside the thick-bordered box on the application form.
Compound of 太 (ふと, 'thick') and 枠 (わく, 'frame, border'). The reading ふとわく is a straightforward combination of the kun'yomi of 太 and the on'yomi of 枠.