A software robot,called a spider or crawler,automatically fetches sites all over the Web,reading pages and following associated links.By design,a spider will return to a site periodically to check for new pages and changes to existing pages.

• 一个叫做蜘蛛或爬虫的软件机器人自动地在整个Web上取出站点，阅读页面和跟随相关的链接。通过设计，蜘蛛可以周期性地返回到站点，检查新的页面和修改已有页面。