Any of a range of relatively high-molecular-weight hydrocarbons (approximately C₁₆ to C₅₀), solid at room temperature, derived from the higher-boiling petroleum fractions [...]

Paraffin waxes have a distinctive crystalline structure, are pale yellow to white (or colorless) and have a melting point range between 118°F and 160°F.

Microcrystalline waxes have a poorly defined crystalline structure, darker color, higher viscosity, and higher melting points — ranging from 145°F to 199°F

Paraffin: (derived from latin parum affinis, [little affinity])
A white waxy substance, resembling spermaceti, tasteless and odorless, and obtained from coal tar, wood tar, petroleum, etc., by distillation. It is used in candles, as a sealing agent (such as in canning of preserves), as a waterproofing agent, as an illuminant and as a lubricant. It is very inert, not being acted upon by most of the strong chemical reagents. It was formerly regarded as a definite compound, but is now known to be a complex mixture of several higher hydrocarbons of the methane or marsh-gas series

source: Webster dictionnary

When you buy paraffin wax to make candles, most of the time it is sold by weight and conditionned as wax pellets. Such a conditioning is ideal as it makes it easy for you to store, manipulate and proportion.

If you live in the United States, chances are you'll never use basic paraffin because there's a wide range of pre-blends available, specially formulated for a specific type of candle. But if you're a beginner, you can learn a lot by playing around with pure paraffin and additives as most european candlemakers have to, due to the unavailability of pre-blends in these countries.

Straight paraffin usually comes with a melting point (MP) of 140°F, which limits its use for "hard" candles like Pillars or Votives.

It comes free of any additive so the odds are great you'll need to add one or several additives, depending upon the type of candle you're planning to make.

But let's start with the beginning: straight paraffin wax is great for the beginner candlemaker and will allow you to familiarise yourself with the different additives, their effect when used in different quantities and also with the ideal pouring temperature in such or such case.

In short: Paraffin wax derived from petroleum, colorless, odourless, unexpensive, widely available (the straight kind, anyway), easy to manipulate, to proportion and to use, can be used with or without additives tp create different kind of candles.