What is it?
Spam is an unsolicited email ro message. Spam is one of the most common items found in an inbox. Spam is when someone sends you junk mail, usually saying "Reply to message to remove from listing." But this is how they trick you. When you reply, you are verifying that the email that they sent the message to was an actual email, and they will sell your email to other spammers. This could also cost a lot of money. If you check email from a mobile device, and the time you spend checking your email was spent looking at spam, it will cost time and money.
How to Avoid it
There are e-mail sights that have spam filters that filter the spam for you, there are also one use email adresses that last for a short amount of time, and when people try to spam it, they will send it to an adress that doesn't exist. Another good way to avoid it is to just not reply.