What on earth does this mean?:

“The purchasers will be required to enter into a covenant obliging the purchases and their successors to title to pay the vendor an overage sum equal to 50% of the uplift in the value of the land for the next 25 years (such an uplift being the difference between the market value of the land immediately prior to a “Trigger Event” and the market value immediately after the “Trigger Event”). The “Trigger Event” includes the following:
a) The grant of planning permission for purposes other than agricultural or equestrian
b) The issue of a Section 191 Certificate (Certificate of lawful use)
c) The issue of a Section 192 Certificate (Certificate of proposed lawful use)
The overage will be secured by a legal charge of the land in favour of the vendor. “
lol! I was just wondering….it’s a property I am potentially interested in

http://www.uklandandfarms.co.uk/search/details.asp?Prop=64420718&Firm=77792&Branch=6&Sys=A&rm=