Both adhesive and iron-on patches are used to apply a patch to a garment. They are different in that they use different materials to adhere to the garment.
Adhesive patches use adhesive to adhere to the fabric, while iron-on patches use heat to blend with the fabric. Pretty simple to tell from the two right? But they both can be sewn as an optional choice.

Stick-on patches are not similar to iron-on patches. Stick-on patches serve the same purpose as iron-patches when it comes to decorations but they do not require any heat pressing. Both are used to apply elements such as decorations or logos to clothing and other fabrics. They act just like a sticker and are pretty easy to remove.
Iron-on patches are usually made from a thin material coated with heat-activated adhesive. The adhesive is activated by the heat of an iron (the same one you use to iron your garments), causing it to become tacky so that it can adhere to the fabric it is applied to.
Stick-on patches are best when it comes to temporary use and are ideal in customizing your items. They aren’t permanent, but can be more flexible compared to iron-on patches. Plus you can even apply them on smooth surfaces like laptops and notebooks, as well as other things like shoes and bags.