Highly optimized meshes, to be used in games, are often called low-poly, or just in-game meshes. Since games are calculated in real-time, we try to preserve resources wherever possible to ensure it still runs smoothly, even on lower hardware setups. The most basic resource we try to optimize is the polygon count of our models. So we only use polygons where they add to the form.
Other important resources are textures, images that are applied to our mesh to add color, surface details, and so on. Game texture sizes are measured in pixels, like other digital images. Their dimensions are, most of the time, defined by power of 2. For example, 256 x 256, 512 x 512, or 1024 x 1024.
A 512 x 512 texture is four times the size of a 256 x 256 texture and will also take up four times the memory, so there are always questions about choosing the right texture size. As a rule of thumb, just think of how big the object will be seen in-game on your screen, to determine how many...