"Brute force" refers to trying all of the possibilities, or at the very least to just trying possibilities one after another until a recognizable answer is reached.
The alternative is to somehow weed out some possibilities without trying them, or to use some kind of "successive approximation" approach to home in on an answer.
An example of "brute force method" would be starting with the first word of an encyclopedia and repeating: read the definition of the current word, and end the loop if you now understand what "brute force" means, and otherwise go on to the next word, continuing one by one from the beginning until the meaning was understood. An example of a non-brute-force method would be using an index to find out which page the "B" words start at, and go to there instead of starting from the very beginning.
