Arm Support
Popular anime poses include "arm support" where characters hold up their own arm. Usually, a character rests their chin on their hand with their elbow on a desk, crosses their arms and holds up their elbow, or leans heavily against a wall or ledge. The basic pose in character design gives an illustration a sense of natural weight and gravity, making the character feel like they are in a real space rather than floating on a canvas.
Artists like arm support poses because they show how someone feels and who they are without speaking. Lounging forward with their head on an arm usually makes a character look bored, tired, or thinking, which is perfect for moody, slice-of-life classroom scenes with the main character staring out the window. However, a character who stands tall with one arm tucked under the other in a modified crossed-arm pose exudes confidence, doubt, or defensive tsundere.
Drawing realistic arm support is difficult technically. The artist must understand anatomy to show how the shoulder rises when weight is placed on the elbow and how clothes bunch and fold around the joint. Wallpapers with this tag are great for figure drawing, relaxed character portraits, and natural body language.