Brewer's yeast is yeast cultured specifically for the purpose of brewing alcohol. Brewer's yeast is sold 2 ways, dry and liquid.

Dry yeast is sold in small packages about the size of a condom wrapper. They usually contain 5 grams of yeast. One package can ferment 1-6 gallons of alcohol. A package of yeast usually costs about one dollar. Dry yeast will last about 3 years but you should try to use it within 6 months for best results. Dry yeast should be refrigerated.

Liquid yeast is a sold in small bottles it contains much less yeast but the yeast in the liquid have a better chance of surviving through less than favorable temperature conditions. Liquid yeast is more expensive than dry yeast.

I brew mead, and to anyone brewing I have had great results with the Lalvin wine yeasts. They have a light flavor and are rather hearty. They produce form 14%-18% alcohol. I use EC-1180 and 71B-1122. Your local brew shop most likely carries these two types. Try them out in your next mead.