Simply said: You will get up to 14 activity every 14 days.
If you post more, you get 14 activity, if you post less, you can get less activity. In addition, if you post say once every two weeks, you do get potential activity. This means in the next weeks you can gain more than 14 activity, as you were active but posted less than the maximum.
Hope this is clear.
Finally i get it lol. Was always wondering what potential activity is.
Yeah NorrisK's explanation is correct.
Like in my situation, I have posted account sales thread here back in 2015, and made some intermediate posts for them, making my account have some potential activity. I had only ~30 activity about a week ago before I decided to join the community again (that's why I had leave with this account with potential activity and sold my old account), and after this post and the activity update, I'll be a Member with exactly 60 activity point if I don't make more posts in the period. In the next 1210000 second period, if I post, I would gain 14 more potential activity.
In a line: The maximum activity cap for a member will increase only 14 in a 1210000 second period (=14d 0h 6m 40s).