Difference between inbox mail and spam mail

Inbox mail is where you receive your ordinary mail, the content is only, what's visible to your eyes, usually the message itself.

But spam mail, aside from the content of the mail, it may contain hidden objects like spyware or adware. Spyware is a program that can spy on your computer activities, while adware triggers pop-ups. It will not harm your computer, but it's sometimes annoying.