Especially during the holiday season when sweet breads abound, you may run across recipes that call for osmotolerant yeast (also called SAF Gold, as it comes in a gold-colored package; SAF is the brand.)
Osmotolerant yeast is a special strain of instant dry yeast that performs better in high-sugar doughs than other yeasts do. In small amounts, sugar enhances fermentation, but when the amount of sugar exceeds about 5% of the flour weight, it impedes fermentation by pulling water away from the yeast. (If you’re a science geek, you probably know that sugar creates osmotic pressure, and if you’re not, you probably don’t care.)
SAF Gold is available from a number of online sources. However, if you can’t get it and have recipe that calls for it, you can use regular instant yeast (SAF Red, for example), and just increase the amount by about 30%.