It is a seek words consisting of 4 squares by 4 squares.
The alphabets that appear are not completely random. It is weighted based on the frequency rate of occurrence in general texts.
For example, 「K, X, J, Q, Z」 appear in 1% of cases, while 「E, S, I, A, R」 appear in nearly 10% of cases.
This makes the word more likely to be formed than if it were completely random.