An infusion is a method of preparing herbs in which 1 to 2 teaspoons of dried herb or 2 to 4 fresh herbs (flowers and berries are substitutable) is “infused” or placed in oil or water (which does not need to be boiled), and then, after about ten minutes, is strained and ingested. 

Things you can infuse include barks (like birch) leaves, and Chinese medicinal teas. 

Here’s a You Tube video section on how to do it: