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Stock Character: A fictional character based on a common literary or social stereotype. Such characters rely heavily on cultural types or names for their personality, manner of speech, and other characteristics and are a key element in genre fiction, supplying relationships and interactions that people familiar with the genre will recognize at once. Stock characters are ready targets for parody, exaggerating the stereotypes associated with them.
So, the 'stock' criminal may be dim and easily apprehended, the 'stock' nurse may be attractive and sexy, the 'stock' policeman not very bright and prone to uttering meaningless jargon, the 'stock' detective able and perceptive but not successful with women. You get the picture.
More honest and perceptive writers tend to avoid the stock character and portray people who appear real instead.