In Proof of Stake, the network (roughly!) allocates rewards for validating transactions based on the amount of coins you have, i.e., your stake in the network.
In Proof of Space, the network allocates rewards based on you proving that you are really storing the data you were supposed to store. If you fail to produce a proof for some data item the network expected you to have stored, you lose the reward.
Another important wrinkle is that Chia’s proof-of-space needs you to prove you’ve stored the right cryptographic noise - rather than, for example, any useful data.
In Proof of Stake, the network (roughly!) allocates rewards for validating transactions based on the amount of coins you have, i.e., your stake in the network.
In Proof of Space, the network allocates rewards based on you proving that you are really storing the data you were supposed to store. If you fail to produce a proof for some data item the network expected you to have stored, you lose the reward.
More info:
https://en.wikipedia.org/wiki/Proof_of_space
https://en.wikipedia.org/wiki/Proof_of_stake