reference number; tracking number; order number
Polite term used in customer service contexts for a number that identifies an inquiry, order, or shipment. The お prefix adds politeness.
See also: 問い合わせ番号
Please enter your reference number.
You can check the delivery status with the tracking number.
Same meaning but without the polite お prefix; used in less formal or internal contexts.
Standard polite spelling with お prefix and full kanji.
Variant with 合せ instead of 合わせ; less common but still seen.
Compound of お (polite prefix) + 問い合わせ (inquiry) + 番号 (number).