The term 'Jack in a Nursery Rhyme' refers to two characters from two different nursery rhymes. The first is Jack SPRAT, who is featured in the nursery rhyme 'Jack SPRAT Could Eat No Fat'. This nursery rhyme tells the story of a husband and wife, Jack SPRAT and his wife, who have opposite eating habits. The second character is Jack Horner, who is featured in the nursery rhyme 'Little Jack Horner'. This nursery rhyme tells the story of a young boy named Jack Horner who pulls a plum out of a pie.