While the 2 terms are often used interchangeably they actually mean different things.
A serving is a standardised, measured amount of food or drink. It can usually be found on the front of food packaging along with other nutritional information.
A portion is the amount of food that you actually choose to eat for a meal or snack. This may be more, or less, than a recommended serving.
Many foods that are advertised as a single portion often contain multiple servings - normally the food label will tell you how many servings the food contains.
If you'd like to find out more the British Heart Foundation has more information about food labels and how to understand the information on them.
You can also find simple advice on how to read food labels attached to this page.