Sometimes its hard to know what words mean. What's inverse kinematics? Well when you want your characters feet to bend to match the angle of a hill, that's Inverse Kinematics (IK)

Let's try this out in real life, go sit on your kitchen floor, now try and reach something on the counter top, but do it so that your arm is locked in an L shape
💪<-- like that

Your hand went over your head right? You feel stupid trusting a stranger on the internet? Okay well your forearm stayed locked to your upper arm as it moved, the arm angle didn't change, considering the potential range of movement in your arm that's smart stuff, that subconscious angle calculation is called Forward Kinematics (FK), to actually reach the object from the country top, we need to try again, but this time unlock your arm and let it reach out as it would.

Your brain 🧠 did the Inverse this time, it calculated the angle of your forearm based on the length of both parts of your arm, the angle your arm needed to be to let your hand grab that thing, that's called IK!