在路径WSUS\更新服务\产品和分类\分类，里面有个定义更新。我不禁疑问这是啥意思？有必要勾选上吗？
pcgeek86表示^[1]："A broadly-released and frequent software update containing additions to a product's definition database. Definition databases are often used to detect objects with specific attributes, such as malicious code, phishing Web sites, or junk e-mail."
我不太明白product's definition database是啥意思，麻烦知道的朋友在评论区告诉我。是产品自定义数据库的意思吗？
根据pcgeek86的描述，我不禁要问，定义更新和安全更新有何区别？