solitaire

A card game to be played by one person, usually played with one or two decks of playing cards. Also known as patience in British English.

Even though there are many such one-player card games, the term is synonymous with one such game known as Klondike, which became more popular after its inclusion (under the name Solitaire) as a standalone game in the Microsoft Windows operating systems starting with Windows 3.0.

Further reading:

• Wikipedia: Patience (game)
• Wikipedia: Microsoft Solitaire