From Ephinea PSO Wiki
Meseta is the in-game currency of PSO. It can be dropped from nearly every enemy and box in the game, and is often given as a reward for completing quests.
Meseta is used to buy weapons, supplies and armor from the in-game shops, as well as to pay for tekking services to identify weapons. Additionally, it can be traded between players for goods and services. It can also be given to Coren, the wandering tekker, to gamble for items.