Delta 8 THC, or D8, is an isomer of Delta 9 THC, which means they are chemically similar. Delta 8 THC is also psychoactive. But the main difference is that D8 is half as potent as regular D9 THC. Thus, it will get you high, but if the effects are easier to handle, you can control them better.
It is harder to green out when using Delta 8 THC. That makes it a favorite of new users and canna-curious.
Also, Delta 8 THC comes from hemp, which makes it legal under the 2018 Farm Bill. But, isomers of Delta 9 THC, like D8, are illegal in multiple states. Thus, you should check its legal status in your area before buying it.