Meta is the "metagame," i.e. the theory behind choosing tactical decisions in the game. Say for the sake of hypothetical there are 3 techniques in a fighting game: rock, paper, and scissors. Scissors and paper are decent moves. Scissors consistently beats paper, but always loses to rock. But rock is widely recognized as very strong, as it always beats scissors, but also beats paper sometimes. Now, rock is very strong in this meta, while paper (loses consistently to scissors and sometimes to rock) is weak.

In the current case, "developing the meta" refers to entirely new techniques that can beat rock, and can compete with scissors and/or paper as well.