Cross-validation???

Question

What's the proper definition of Cross-validation?

Answer 1

https://machinelearningmastery.com/k-fold-cross-validation/#:~:text=Cross%2Dvalidation%20is%20a%20resampling,k%2Dfold%20cross%2Dvalidation.
https://en.wikipedia.org/wiki/Cross-validation_%28statistics%29

Answer 2

thank you @Samsil Arefeen