Solitaire is a classic card game that was included with early Windows PCs and involves arranging cards according to suit. The document discusses Solitaire for Mac, a version of the game adapted for Mac users that includes over 55 different solitaire games like Klondike, Spider, and FreeCell. It can be downloaded from the website http://www.solitaireformac.org, where users can access and play various types of solitaire games on their Mac computers.