Means a mistake is not serious and often pardoned due to its minor nature. Her habit of being a few minutes late was considered a peccadillo by her otherwise punctual nature.
Pro Tip 2/3
Informal Usage
Used in casual or informal conversations, not normally in formal writing or speeches. He brushed off his missed call as a peccadillo, not worth fretting over.
Pro Tip 3/3
Subjective Significance
What one sees as a peccadillo, another might view as a more severe issue. To the strict supervisor, an untidy desk was more than a peccadillo.