You've learned 1D DP. define states, write transitions, and reduce space. These problems all had one-dimensional state: position in an array.
But some problems need more. What if you're comparing two strings? You need to track positions in both. That's 2D DP.
What if you have a grid and need to track row and column? Again, two dimensions.
In the next section, you'll see how the same patterns scale up. States become instead of . Transitions look at more neighbors. Space reduction gets trickier.
The good news: everything you learned still applies. 2D DP is just 1D DP, done twice.