What it is and where it comes from
A "natural flavouring" is made from natural raw materials: fruit, spices, herbs, but also meat, chicken fat, dairy or fish. It is often dissolved in alcohol or glycerin. Meat and savoury flavours are the most likely to be animal based.
Where you find it
Almost every processed food: crisps, sauces, sweets, drinks, ready meals and snacks.
What to look for on the label
A halal logo or a vegan label settles it. For savoury products, check whether a meat flavouring is named. For sweet products the main question is alcohol: see alcohol in flavouring.
This is a guide, not a fatwa. Recipes change, so check the label, look for halal certification, and ask your local imam where scholars differ.