Vocabulary - Sliding Window

A sliding window maintains a contiguous subarray that "slides" through the array. You track the window using two pointers: $left$ and $right$. There are two variants:

$1.$ Fixed-size window: the window always has exactly $k$ elements. You slide it one position at a time.

$2.$ Variable-size window: the window grows and shrinks based on some condition. Both achieve $O(n)$ by processing each element at most twice: once when entering the window, once when leaving.