The term 'poster gradient composition' refers to the use of gradients in poster design, where gradients are used to blend colors or shades smoothly across the poster. This technique can create visual depth and interest, often used in advertising and graphic design to draw attention and convey a sense of motion or progression. Gradients can be linear, radial, or angular, and can be applied to backgrounds, text, or other elements to enhance the overall aesthetic of the poster.