If a sticker or material is splash-proof, it means it can handle droplets of water hitting its surface.
It cannot handle being soaked or submerged in water for even short periods. It also cannot come into contact with oil. Oil can stain some materials, mainly paper materials.
As a general rule, papers are sometimes splash-proof or not suitable for any contact with liquids. In contrast, plastics are usually either splash-proof or waterproof.
Our biodegradable paper stickers are an example of splash-proof stickers.