- Someone not directly involved in a transaction; an entity beyond the seller (first party) and customer (second party).
- A seller may employ a third party to perform specific services to augment the value of a product, such as packing and distribution.
- Someone only incidentally or tangentially connected to an incident or dispute; someone other than the principals; a bystander or independent witness.
- A political party in opposition to the main parties in a two-party system
- French: tiers (rare: tierce partie)
- German: Dritte
- Portuguese: terceiros
- Russian: тре́тье лицо́
- Spanish: terceros
- French: troisième parti