Isometric graphics in video games and pixel art are different ways of showing pictures that make them look like they have three dimensions. You know how a picture on a piece of paper looks flat, like it doesn't have any depth? Isometric graphics and pixel art are different ways of making pictures that look more like they are popping out of the paper.
Isometric graphics are often used in video games to show a map or a world. The pictures are drawn at an angle, like birds-eye view, so you can see everything on the map. The pictures are also made to look like objects are farther away by drawing them smaller. For example, mountains in the distance would be smaller than a house close up.
Pixel art is a type of art made by using pixels or tiny squares. Think of them like building blocks. Artists take these little squares and put them together to make an image. The more squares they use, the more detail you can see in the picture.
Both isometric graphics and pixel art are used to make video games look more interesting and fun to play. They help make the game world look more realistic and immersive.