[sinstein]

Ownership: All intellectual property rights in and to the User Content are and shall remain your property, and Grammarly shall acquire no right of ownership with respect to your User Content.

Link - https://www.grammarly.com/terms#ownership

[brobdingnagians]

That is in regards to ownership; it is true that you would still own the content, but they get an irrevocable, worldwide, royalty free, sublicensable, and transferrable license to use it.

[sinstein]

But use it to improve the underlying algorithm/service. I don't think they have a license to publish or sell any User Content.