This is the literal dirt, soot, or grime that soils a surface. Think of a muddy smudge on your clean white trousers or a blemish made by dirt on a pristine wall.
In her book “Shrinking the Smirch,” psychologist Jo Johnson uses the term to describe the negative internal "voice" that tells us we aren't good enough. Instead of letting it grow, learn to "shrink" it by practicing self-compassion and Acceptance and Commitment Therapy (ACT) . smirch
(verb): To make something dirty, stained, or discoloured. Smirch (noun): A stain, blot, or blemish on someone's reputation or character. This is the literal dirt, soot, or grime