Adobe Illustrator

A vector graphics editor ... The preferred software for Illustrators and Graphic Artists. You can scale the artwork to any size (from business card to full scale billboards) without sacrificing the resolution.

Raster vs. Vector

a really good (short) video explaining the difference ...

Introduction to Illustrator 

Vector Art
Advantages include:

• Scalable Art
• Crisp/Sharp lines
• Print Hi-Resolution
• Smaller file size
• Good for drawing illustrations

 Disadvantages

• Drawings look flat (cartoon like)

• Photo-realism is not usually possible 

The Interface