(pattern) => pattern.test(str) is the callback function you are passing into some(). pattern is just the name you have given to the first argument that is automatically passed into the callback function (you could have called it anything, but I think pattern makes sense here). Seeing as validPatterns is an array of JS patterns and you are calling the first argument pattern, what do you think pattern is?
Adding to what @bbsmooth said, that argument will represent any element in an array. The method .some() will check if at least any or “some” element from the array satisfies certain condition.
Let’s say we have an array of numbers, called nums like this: [2,3,5,6] and we want to test if there is an element above 3; then we can do it using the method as shown below:
nums.some(n => n > 3)
It will return true because the array contains one or more elements that satisfies that condition. Hence, you can name the argument to whatever you want and it will always takes into account the element.