Sizz is a relatively new aesthetic that focuses on noise, distortion and other artifacts as a way to modify the subject of an image and make it more abstract. Though named in 2017 following a trend found on sites like Tumblr and Instagram, sizz is in fact a more modern evolution of several older aesthetics - a sort of combination of the German expressionist method of abstraction to build a sense of mood, the emotion created by contrast and lighting in American film noir, and the way the Japanese are-bure-bokeh street photography movement embraces griminess and lack of focus in its snapshots. The term "sizz" is intended as onomatopoeia to simulate the sound of noise - according to Merriam-Webster, the word "sizz" means "to hiss or move with a hissing sound."
Sizz is defined not by a set of specific rules, but by an "ethos" - composition is valued over technique, experimentation over purity, and feeling over formula. The community around this aesthetic is centered primarily around appreciating the artists that create such works, so giving credit is considered mandatory. (Most of the information on this page, for example, is taken from this post made by the creator of the aesthetic.)