[Nerull]

A blackguard is a prestige class. In 3rd edition, they have prestige classes that you can qualify to take levels in. Any class can qualify to be a blackguard; they just have to have an evil alignment, and need to have the required feats, skills, etc.

Blackguards are essentially evil paladins, with twisted versions of many of the paladin powers. They need not have been paladins before; nothing is stopping a wizard, bard, etc. from qualifying for blackguard. They get divine spells as they rise in level (similar to a paladin), and the number next to the class name in the spell is the spell level of that spell on the Blackguard's spell list. In your example, the spell would be a 3rd level spell for wizards and sorcerers, and a 2nd level spell for blackguards.