Espresso powder is dehydrated brewed espresso. Espresso powder is typically used for baking cakes, brownies, cookies and other desserts that use chocolate. Espresso powder is an instant coffee, but it is typically not used to brew coffee for drinking.
Espresso powder is typically found at any grocery store. Cooks can make homemade espresso powder by drying and grinding espresso beans before crushing them into a fine powder. A dark roast instant coffee can be substituted in most recipes that use espresso powder, but the flavor may be slightly different. Cooks can also substitute very finely ground espresso or coffee, but the amount used should be reduced.