Pirate

A Pirate in the world of One Piece is anyone man woman or child, who raises a Jolly Roger, whether they commit an act of Piracy or not. This is not, however, usually is not enough to give anyone a bounty but is enough to be arrested by the Marines. There are two types of Pirates in One Piece, but the terms were only in the original Romance Dawn chapter, and have not yet been mentioned in the current version of One Piece.

Mountain Bandits are said to be the opposite of Pirates and have not been known to get along with each other too well.

Types of Pirates
First mentioned in Romance Dawn V.1 the two main types of pirate are the Peace Maine and Morgania. These terms were once again mentioned in Romance Dawn V.2, however they are not mentioned in One Piece itself. This is largely due to the fact most pirates are a combination of both Peace Maine and Morgania ideals.

Peace Maine
Described in Romance Dawn Version 1, A Peace Maine is a Pirate who goes on adventures, and doesn't really care about personal treasures or going aorund fighting other Pirates. Luffy is a reall good example of a Peace Maine.

Morgania
The Morgania fight for treasure and personal gain. They are greedy and love to fight just to cause other people pain and misery. Most of the other Pirates Luffy and his Crew meet are Morgania. Luffy dislikes Morgania and only wants to recruit Peace Maine Pirates.

The 4 Blues
Generally outside the Grand Line, most pirates are considerbly much weaker then those inside. Often they are left untouched by the Marines because their attention is drawn towards the Grand Line rather then the East, West, North and South blues.

Thats not to say they don't have their share of villianous pirates, even in the weakest of the blues, the East Blue, powerful men like Don Krieg and Arlong were found. Generally few people in the four Blues have access to Devil Fruits or general knowledge on them. Most Pirates seen before the Straw Hat crew entered the Grand Line used weapons in some form.

The Grand Line
While there are individual pirate crews roaming the Grand Line, the more powerful pirates reside in this sea. These are namely the Shichibukai and the Yonkou.

Generally, the weaker pirates are often weeded out by the Marines or Shichibukai before they can get any further. The unfortunate ones don't even make it to their first island due to a lack of understanding on how the weather works on the Grand Line. The Grand Line is where your most likely to see Devil Fruit users, both in and out of pirate crews.

In the second half of the Grand Line the most powerful pirates are the Yonkou. The second half of the grand Line (dubbed the "New World") is their playground and it forms a rather dangerously balanced part of the One Piece world.