Mathematically, the term "fold" is not related to the application.

In a brief, fold means portion or fraction.

You can get the percentage by dividing 100 by the fold.

For example 5-fold=100/5=20.

So each fold contains 20, and 1 fold will be used for validation. so 80% will be used for training and 20% will be used for validation.

Similarly, 10-fold=100/10=10.

So, 90% of data will be used for training and 10% will be used for validation.