What infuse means
To infuse means to steep a flavouring ingredient in a liquid or fat so that its flavour, aroma and sometimes colour pass into it. The flavouring is usually removed afterwards, leaving the liquid infused with its character. It is a gentle, simple technique used throughout cooking, baking and drink-making. Common examples include warming milk or cream with a vanilla pod, cinnamon stick or citrus zest before making custard, ice cream or panna cotta, soaking saffron threads in warm water or stock before adding them to rice, steeping herbs, garlic or chillies in oil, and simmering spices or herbs in sugar syrup for cocktails and desserts.
Making a cup of tea is itself an infusion. Heat speeds up infusing, which is why many recipes bring the liquid to just below a simmer, add the flavouring, cover and leave it to stand. Cold infusing is slower but gives a fresher, more delicate flavour and is used for things such as cold brew coffee, fruit waters and some syrups. The strength depends on the amount of flavouring and how long it steeps, so tasting is the best guide.
Over-steeping can make some ingredients bitter. You will see the instruction to infuse in recipes for custards, sauces, syrups, oils, drinks and desserts.