Vocabulary - 2D State

A 2D (two-dimensional) DP state uses two indices: $dp[i][j]$. Each combination of $i$ and $j$ represents a unique smaller problem to solve. For example, $dp[3][5]$ might mean "the answer when you've processed $3$ items and used weight 5." You can think of it as a table. Rows are one dimension, columns are another.

Each cell stores the answer to one specific subproblem. The base cases initialize some cells (often $dp[0][0]$ or the first row/column), and the final answer comes from a specific cell or a combination of cells.