GridCaptch is new type of CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) which adds as an additional layer of security.
It is a type of challenge-response test used to determine whether or not you are human.
How this works?
It consists of a letter and a number that identifies a row and column on your target grid. The combination of a row and column where they meet is called a coordinate.
Take this one for example:
In this case, the given coordinate is "H8".
First, search for the "H" in the grid.
Now, search for the "8" in the grid.
Look where they meet...
Ticking this cell will validate you are human.