Firstly, I think it will be better if I define the two keywords involved which is "Curation" and "Rewards" to make my answer more comprehensible and understandable.
Curation simply means the act of giving someone something that has to do with monetary value. In the Steemit realm, Curation occurs when you upvote other people's posts or when your post get upvoted by others in which you earn some certain amount of money, this shows that you have been curated. There are different ways of getting curated on the steem blockchain which can either be from communities like #curie, #airhawk-exchange , and many others we all know about. You may also get curated by using some #dApps on the steem blockchain which rewards you for your activity using their apps or platforms.
Rewards is the act of you getting paid. It involves you getting something in return. If I was to define reward using Steemit, I would define reward as the upvotes or monetary rewards you earn from your activities on the steem blockchain. These activities includes your blogging activities, vlogging, etc and other activities you engage in just to earn steemit rewards (steem, SP and SBD).
Curation reward in Steemit is that special reward that is paid to people who upvoted your posts. This is why the steem blockchain has a reward system of 50/50 and 100% power up. The 50/50 reward system enables other people to earn from the Curation rewards just also like the 100% power up system. The Curation rewards are mostly in the form of SP.
In conclusion, Curation reward is that reward you earn from Upvoting other people's posts just like others earn it too when they upvote your posts.
Thanks for reading and I hope this helps.
In Steem ecosystem when you upvote a content you are known as curator. There is a reward pool in Steem ecosystem which comprises of author reward, curator reward, block producer reward, etc.
In Steem blockchain the split of the reward is 75/25, means 75% of the post earning will go to Author(minimum) and 25% of the earning will go to curator(maximum). The curation reward further varies significantly if you vote within 0 to 15 mins of the post.
In HF21, it has been proposed to change the share of author/curator to 50/50 in stead of 75/25. If the proposal gets super majority then it will be enforced in Steem blockchain and the new rule will come into effect post HF21.
If you have decent amount of SP, you can earn good amount of curation by selectively choosing quality posts which is likely to earn more. But in order earn maximum curation reward it is necessary to time the voting in such a way that you must vote before the whales so that you can maximize your curation reward.