Spam email and junk email can be the same however sometimes legit email gets sent to the junk email folder.
But mostly spam email and junk email are the same thing as junk mail and spam mail can be mass email sent out for advertising through spamming.
But sometimes like I said you might have a legit email get accidentally sent to the junk email folder so if you're looking for an email such as a password reset etc and haven't gotten it in your regular email inbox then you should check the junk mail folder.
But Junk mail and spam email can be the same thing.