Kernel functions are used in machine learning including support vector machines to increas non-linear diversity. The term originates in mathematics where a postive definite kernel is a form of non-linear generalisation of the inner prooduct.
Used in Chap. 7: page 107; Chap. 8: page 113
Links:
Wikipedia:
Kernel method
Wikipedia:
Positive definite kernel
turing.com:
Designing of Different Kernels in Machine Learning and Deep Learning