Is definitely join these group a correct grammar?

No, "Definitely join these group" is not grammatically correct. Here's why and how to fix it:

* Missing Article: You need an article before "group" ("the" or "a").

* Plural/Singular: If you're referring to more than one group, "groups" is the correct plural form.

* Verb Tense: The phrase lacks a verb. You need a verb to complete the sentence.

Here are some corrected options:

* "Definitely join these groups." (If there are multiple groups)

* "Definitely join this group." (If there is only one group)

* "You should definitely join these groups." (More polite and complete)

* "I definitely want to join these groups." (More personal)