摘自wikipedia：https://en.wikipedia.org/wiki/Magic_number_%28programming%29#Examples

In computer programming, the term magic number has multiple meanings. It could refer to one or more of the following:

• A constant numerical or text value used to identify a file format or protocol; for files, see List of file signatures
• Distinctive unique values that are unlikely to be mistaken for other meanings (e.g., Globally Unique Identifiers)
• Unique values with unexplained meaning or multiple occurrences which could (preferably) be replaced with named constants

例如BMP图片文件的前缀是“BM”，JPEG图片文件的前缀是“JFIF”，这些文件的前缀就算是Magic number，这是指上面的第一种情况。再如Linux系统使用的uImage压缩内核的前缀是：0x27051956，这个就是uImage的Magic number，属于上面说的后面两种情况。三种情况都有共同点，都是用来作为区别事物的，一般用于程序检测文件类型做对应的处理工作。