Items are food products that are sold by the restaurant and are available in the menu. An item contains information like price, product description, food type, and image.
Items can further be sorted based on categories depending on the course of the meal. An item can further be customized to suit the customer's preferences by adding customization (Reference link: How to add customization?).
Here is an image that shows items on Zomato:
In the above image, Margherita, Classic Corn, and Classic Tomato are all items under the category: Veg Pizza.
Aggregators use tags like Bestsellers, Must-Try, Today's Exclusive, etc to tag items to make a few items from the menu stand out, therefore boosting sales for these items.
Here is an image that shows items tagged as Bestsellers by Swiggy: