Most of the time, the path of the mage is long and boring. Not everyone has the patients to study for years on end just to be able to cast a fireball, but not everyone possess the natural talents of a Sorcerer or the divine blessings of a Cleric. The bold few, take a short cut to greatness.
Warlocks are mages who form pacts with other worldly entities. Spirits of the fey, or beings claiming to be gods are typical, and the price is often too high for most, but the benefits are well worth it for others. Most Warlocks have a negative reputation, as pacts use to be made with demons and other dark beings. It doesn't help that most cults are usually led by a Warlock, seeking to expand their influence and power.
Most the time, arrangements require the Warlock to do something for the entity, or give somethings of themselves of equal value. This can range from a few fingers to one's soul. Other times, it can be a simple arrangement of master and apprentice, allowing the Warlock to study directly from a magical being instead from old books. This allowed the Warlock to focus more on what they call "practical magic" instead being stuck in a library for days on end.
In present day, the most people have a mixed view on Warlocks. Mostly viewed negatively, given reputation of cults, and that other mages see them as "cheaters". But the reality is that spirits, demons, and other entities don't just make pacts with just anyone. They will ignore most, even powerful mages in a lot of instances, but when they do make a deal, its with someone they believe is worth the effort to reach out to.