An adventurer is someone who earns their wage by completing 'quests' or bounties. Generally, these tasks are listed in an "Adventurers Guild." Adventurers generally fight in groups (and even if the individuals in a group are very weak, a group is ranked according to their total efficiency, rather than the efficiency of each individual). In other words, a group could include a Silver-Ranked adventurer and still be considered a Gold-Rank group.
Although the system varies depending on the area, in the continent Liscor resides in, Adventurers are separated by several divisions:
Bronze-Rank - These adventurers are the weakest of the lot - People who have only recently become adventurers are considered Bronze-Rank.
Silver-Rank - Experienced adventurers. The power of a Silver-Rank is far above that of a Bronze. It is said that a team of that rank are more than a match for a small city's standing militia. The equipment and magic available to such groups allows them to take on challenges even a large garrison might not manage. The People who are considered Silver-ranked are mostly in the low 20's at best.
Gold-Rank - These are hardened adventurers, who are anywhere from Level 24 onwards. Unlike Silver-rank adventurers, they tend to have rare magical artifacts that greatly boost their prowess. Because of these special magical items, they are considered to be far above Silver-Rank. At the top of that group, teams of adventurers are equivalent to small armies and could affect disputes between nations. While the gear is one of the most deciding factors for becoming a Gold-rank, once Level 30 has been reached one could call oneself a Gold-rank regardless of the gear.
Named Adventurers - World-famous adventurers. If an adventuring party or individual reaches that level of renown they were no longer ranked. Instead, they are known as Named Adventurers because their names are known throughout the part of the world where they travel. They are living legends to adventurers. These adventurers are some of the strongest in the entire world. Adventurers seem to be recognized as Named ones starting from around Level 40.
- Some countries have ranking systems that extend beyond the gold rank into platinum, adamantium, and so on. 
- It is the whole group that gets the rank. So just one member of a party needs to reach, for example, the Gold-Rank for all of his group members to get it as well, without meeting the actual requirements. Therefore a rank doesn't reflect the actual strength.
- Pirateaba mentioned in Erin's "Guestbook" a Gold-Rank adventurer that was a Level 42 [Pyromancer]. Another "Guest" pretended to be a Named Adventurer, telling all that he is a Level 44 [Mage], while actually being a Level 14 [Scoundrel]. That shows that one can become a Named Adventurer in the mid 40's, though it is not clear if that would make that person a very weak one, as the earlier mentioned Gold-Rank had a very similar level.
- Gold-Rank adventurers or higher can earn as much as 4,000 gold coins if they are lucky in a dungeon.
- The adventurer guilds' standards have decreased immensely over the years, shown by Teriarch thinking that a Silver-rank team that's nearing the Gold-rank to be only a Bronze-rank group.