Content, Cost, and Time
What is it?
Spam is an email or text that has been sent out to a mass amount of people. Not only does it cost money / take up bandwidth, but the content can contain malware or fraud. An example of this can be an email posing as a bank asking for account details.
How to Avoid it
It is easy to avoid spam. The most effective ways to protect your email is to set up filters. However, if you want to sign up for something, you can create a temporary email that automatically deletes itself. If you do get spam, the most important thing is that you do not reply! This confirms that the email exists, and can be sold for more money to other spammers.