Clinical trials - recruiting def.
Not yet recruiting: The study has not started recruiting participants.
Recruiting: The study is currently recruiting participants.
Enrolling by invitation: The study is selecting its participants from a population, or group of people, decided on by the researchers in advance. These studies are not open to everyone who meets the eligibility criteria but only to people in that particular population, who are specifically invited to participate.
Now that they are done enrolling 210 by invitation... That is, selecting a diverse trial population. Hand picked by age, gender, and race... to achieve undeniable results. Now they open it up to Joe Shmo.