Spam traps are emails that can instantly ruin the reputation if given the chance. Those emails are provided by email providers. If those emails find their way on a list they and someone sends an email to them, they will block your email over an entire network once they see you have sent an email to a spam trap. Spam traps are collected through several means such as bots or humans, or they can easily cover their way in an purchased email list. But if you are interested to learn more, you can find it out on Zerobounce's page article for Spam traps, they have a very detailed page about the spam traps and what you can do to avoid them and are also an email validation service, so you can hit two birds with a single stone. (Here is the link https://www.zerobounce.net/spam-traps.html)
Greylisted emails on the other hand are a safety measure against the first type. It is a measure mostly offered by email sending services that will decline the first email that come through from a previously undentified user. After a solid amount of time and a great check, your email will make it's second attempt into your target's inbox if your email have not been already flagged as spam. Sending multiple emails to this type of service may greatly downrank the reputation of your email and thus your next sending emails will find their placle in the spam folder instead of the inbox.