网络信标（web beacon），又称网页臭虫（web bug），是可以暗藏在任何网页元素或邮件内的1像素大小的透明GIF或PNG图片，常用来收集目标电脑用户的上网习惯等数据，并将这些数据写入Cookie。网络信标在邮件跟踪和垃圾邮件中较为常用。

网络臭虫（Web bug）也称为网络信标（Web beacon）是一个放在网页或电子邮件上的文档对象，用于监测用户的行为。 不像Cookie可以被浏览器用户接受或拒绝，网络臭虫只是以图形交换格式（GIF）或其他文档对象的形式出现。 它通常只能被检测，如果用户查看网页的源版本会发现一个从不同的Web服务器而不是从网页的其他部分负载的标签。

A web beacon is an object embedded in a web page or email, which unobtrusively (usually invisibly) allows checking that a user has accessed the content. Common uses are email tracking and page tagging for web analytics. Alternative names are web bug, tracking bug, tag, or page tag. Common names for web beacons implemented through an embedded image include tracking pixel, pixel tag, 1×1 gif, and clear gif. When implemented using JavaScript, they may be called JavaScript tags. There is a work in progress to standardize an interface that web developers can use to asynchronously transfer small HTTP data from the User Agent to a web server that call it simply beacons (in the context of web development) which can be used to send data to a web server prior to the loading of the document without delaying the load and affecting the perception of page load performance for the next navigation.