A padded bra has padding in the base of the cup to lift your breast and give the appearance of larger breasts. Padding can also refer to a light padding through the cup to hide any nipple shape, but usually when people talk about a padded bra they are meaning the type that makes your bust look larger.
Padded bras come in a variety of different shapes and styles, they could be t-shirt bras, demi cup, push up or a combination of shapes. Whatever style they are you won’t be able to tell from looking at them on if they are padded or not.
The padding can be made of a variety of materials, some are foam or silicone rubber, others use gels and liquids that shape to your body and will feel more like real breasts. The padding is removable in some bras, a pocket is built into the base of the cup so you can easily take the padded inserts in and out.
Even though your breasts will look like a larger cup size when you wear it you still buy the same size that you are normally. This is different from it you are buying a non-padded bra and have separate inserts that you are using, in this case you will need to get a larger cup size to fit them in.