Amigurumis are stuffed animals made through crocheting.
They come in many different sizes depending on the size of your hook and weight of your yarn. Many people would reccomend going for a thinner yarn and smaller hook to create tight stitches, which will make your finished toy have less gaps between stitches. This will help avoid seeing the stuffing inside and will result in a smaller toy.
However, there's nothing wrong with going big. There's no real difference between both sizes as long as you keep the stitches tight and neat when working on both. Making big amigurumis is just as fun and just as adorable.