Often-memorized string: Abbr

• Nine digits: Abbr.
• Tax form ID (Abbr.)
• Nine-digit identification: Abbr
• ID with two dashes
• Taxpayer's ID
• Fig. on a W-9
• Digits used for employee identification: Abbr
• Datum on an IRS form
• Frequently used ID

Wikipedia Word definitions in Wikipedia
SSN may refer to: