What you wear to an office party depends on where and when the party is being held.
At the workplace after work
Both men and women can simply show up in the clothes they have worn all day, or they may opt to change or dress it up a bit.
Outside the office
Generally, both men and women change into dress clothes. Because the event is a business one, overly dressy or revealing clothing is in poor taste. It’s better to err on the conservative side. If you are unsure about what to wear check in with the event coordinator or a colleague who has attended these social events in the past.
The name tag: a must wear accessory
Wear your name tag if the function calls for them. Name tags are both necessary and useful at business functions attended by people from other departments or businesses.